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STATE OF FLORIDA
STATE BOARD OF CONSERVATION
Ernest Mitts, Director
FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director
GEOLOGICAL BULLETIN NO. 41
'OME GEOMORPHIC FEATURES OF CENTRAL
PENINSULAR FLORIDA
by
WILLIAM A. WHITE
SP-
U Published for
THE FLORIDA GEOLOGICAL SURVEY
Tallahassee, August 15, 1958
FLORIDA STATE BOARD
OF
CONSERVATION
LeROY COLLINS
Governor
R. A. GRAY
Secretary of State
RICHARD ERVIN
Attorney General
J. EDWIN LARSON
Treasurer
RAY E. GREEN
Comptroller
THOMAS D. BAILEY
Superintendent Public Instruction
NATHAN MAYO
Commissioner of Agriculture
ERNEST MITTS
Director of Conservation
LETTER OF TRANSMITTAL
lorda geological Survey
'Callaiassee
May 27, 1958
MR. ERNEST MITTS, Director
FLORIDA STATE BOARD OF CONSERVATION
TALLAHASSEE, FLORIDA
DEAR MR. MITTS:
The Florida Geological Survey proposes to publish as Geological
Survey Bulletin 41, a paper written by Dr. William A. White,
Professor of Geology, University of North Carolina, Chapel Hill,
North Carolina, entitled "Some Geomorphic Features of Central
Peninsular Florida." The paper discusses various changes in
stream patterns and their association with land forms of Florida.
The changes of these streams record certain features of the
geologic history which bear on the interpretation of our
stratigraphy and geology, and will be useful in a search for
additional heavy minerals. Such data also provide new leads to a
correct interpretation of our geologic history.
Respectfully yours,
ROBERT O. VERNON, Director
Completed manuscript received
November 25, 1957
Published by the Florida Geological Survey by
E. O. Painter Printing Company
DeLand, Florida
August 15, 1958
TABLE OF CONTENTS
Acknowledgments ---------------....--------........ --
General landforms----------- - ..
The Lake Wales Ridge ......--..-
The Winter Haven and Lakeland ridges --- --- -- --
The Brooksville Ridge --- ------------
The Orlando Ridge -.-. --------------.----------.
Drainage of the Florida Peninsula
Trenching and drowning of coast-parallel streams -----_
The Withlacoochee River --------------......-
Drainage of the area between the St. Johns and Kissimmee rivers
Relict beach ridges as index to sea level change and subsidence
Relict beach ridges in Osceola and Orange counties ------
Relict beach ridges in Polk and Lake counties -------
Oklawaha valley --
Dunes along the eastern foot of the Lake Wales Ridge ---
Drainage of the Lake Wales and Lakeland ridges ---- ---
The cross-peninsular divide .....................-----------
Offshore sedimentation in the Gulf of Mexico --..----
The question of westward tilt in the Florida Peninsula ---
Evidence for tilted terraces ----
Evidence of tilting from west coast estuaries ..------------------
Drowned karst ------ ------------.........................-------
Coastal re-entrant between Appalachicola and Anclote Key --
Submergence of the west side of the Florida plateau ---
Evidence from the Everglades --------------------.--
Page
7---
-- 9
...- 10
10
-- 10
.. .. 10
11
17
- 19
-- 27
33
34
35
38
38
--44
-- 45
52
53
54
--. 56
62
........--- 62
62
63
.......- 63
----- 63
Florida lakes --.....------------- ----
Shallow lakes ------ ..--------.....
Influence of local relief in forming lakes -......-----
Aligned swampy sinks controlled by beach ridges ----
Lakes along the terrace scarp in Citrus and Levy counties ---
Lakes in the periphery of the Chiefland Limestone Plain ---
Lakes along the Lake Wales Ridge _- -- --------
Lakeless limestone regions, the Everglades .......--------------------
Comparison of Florida lake country with Highland karst elsewhere
Characteristics of zone in which large lakes occur ---------.
Relation of large lakes to structural highs in the Miocene sediments
Wasting of lake water .------- -- ------- .... --...---
Relation of lakes to piezometric surface --------------.
Summary ....- --- ----------------
Influence of deep circulation -- -..--------- ---.---.--
References cited ... ... --------. ------...-
Glossary of geological terms used in this report --.
S65
-- 66
- 73
74
75
76
S76
.-- 77
S80
80
S82
.-- 83
84
S86
.-- 86
S91
S92
1..1..
- -- - -- -
ILLUSTRATIONS
Figure Page
1 Aerial photographs of part of Polk and Lake counties showing
beach ridges increasingly obscured by solution subsidence toward
the north _-- .-- --. ----- Between pages 12 and 13
2 Profile of Withlacoochee River --..----------- Between pages 22 and 23
3 Part of planimetric map of Pasco County showing diffluence of With-
lacoochee and Hillsborough rivers ..--....... ..-------------.--- 28
4 Aerial photograph of area in southeastern Pasco County showing
diffluence of Withlacoochee and Hillsborough rivers --------- 29
5 Aerial photographs of part of Osceola County showing beach ridges 32
6 Aerial photographs of southwestern part of Highlands County show-
ing southeastern end of Lake Wales Ridge and dunes along the east
side of the ridge .---..... ---------... --------- .---. 40
7 Part of Babson Park and Lake Weohyakapka sheets showing dual
direction of elongation of dunes --------------- 41
8 Northwestern corner of Jupiter sheet showing dunes formed along
present peninsular east coast --- ..--------- 42
9 South-central part of Childs sheet showing dune zone and terrace
escarpments -.-----------... -....--.--....---- 43
10 Map showing thickness of Miocene sediments in relation to large
peninsular lakes ------ Between pages 46 and 47
11 Aerial photographs of eastern Brevard County showing beach ridges,
False Cape, and Cape Canaveral _------------------- 50
12 Map showing bottom sediments off the west coast of the Florida
Peninsula ---------...-...-.--...........------- 53
13 Northeastern part of Deer Park sheet showing Pamlico scarp with
crest at elevations approximating 45 to 50 feet .. ------------ 55
14 Map showing contours on the rock floor of the Everglades -----...- 64
Plate Page
1 Drainage map of central Florida _--------- Between pages 20 and 21
2 Drainage map of typical area between St. Johns and Kissimmee
rivers _--..-.----------.-... --...-...--.. --------- 30
3 Map showing dune areas along eastern side of Lake Wales Ridge
Between pages 38 and 39
ACKNOWLEDGMENTS
I would like to express my appreciation of the many kindnesses
of Dr. Herman Gunter, former Director, and Dr. Robert O. Vernon,
Director of the Florida Geological Survey. The wealth of geological
information offered by Dr. Vernon has supplied much of the data
which made possible many of the conclusions of this report.
Hypotheses presented in this report were discussed with Dr.
Richard A. Edwards, University of Florida, Gainesville, and his
critical comment was a great assistance.
Mr. Archibald O. Patterson, Florida District Engineer, Water
Resources Division, U. S. Geological Survey, kindly made available
information concerning discharge in certain streams and lakes. Mr.
A. Tabita, Chief, Hydrology Section, U. S. Army Corps of Engineers,
Jacksonville, supplied profiles of streams. Mr. Victor E. Muse, also
of the U. S. Army Corp of Engineers, was very helpful in supplying
data from his observations in the Everglades.
GENERAL LANDFORMS
Several geologists have contributed to the classification of
Florida topography. Matson and Sanford (1913), Fenneman
(1938), Cooke (1945) and Vernon (1942, 1951) all have described
the general landforms and subdivided the State into physiographic
units based on topographic and geologic distinctions.
Matson and Sanford divided the central peninsula into four
sections, all of which parallel the present coastlines. Named in order
from west to east, these were: (1) "Flatwoods or Hammock Lands"
along the Gulf Coast; (2) "Lime Sink Region" somewhat inland
from the Gulf Coast; (3) "Lake Region" along the axis of the
peninsula; and (4) "East Florida Flatwoods" along the Atlantic
Coast. These divisions seem to have been accepted by Fenneman
(1938), who presents excellent brief descriptions of them.
Cooke (1945) offered a more succinct classification of landforms,
using only two categories to describe the peninsula. These were the
"Central Highlands" along the axis of the peninsula and the
"Coastal Lowlands" along its periphery. Cooke's "Central High-
lands" included most of Matson and Sanford's "Lake Region" and
"Lime Sink Region."
Vernon (1951, p. 16) stated:
"The physiography of Florida can be grouped logically into four general
subdivisions on the basis of origin. Highlands are composed of either
sediments formed as a part of a high-level, widespread, aggradational
delta plain or of Tertiary land masses rising above this plain. Lowlands
have been formed either by deposition and erosion along coast lines by
marine agencies or by alluviation and stream erosion along stream
valleys. These obvious land forms can be grouped under four sub-
divisions of the Coastal Plain Province, namely The Delta Plain
Highlands, The Tertiary Highlands, The Terraced Coastal Lowlands,
and The River Valley Lowlands. These terms, applying to major
subdivisions of the physiography of the State, can be subdivided to
any degree and local names can be applied."
Some confusion might result from the use of two terms, Tertiary
Highlands and Delta Plain Highlands, for there are delta plain
deposits that have been dated as Tertiary in age (Vernon, 1951,
p. 184, 185; Bishop, 1956, p. 28). For the purposes of this report,
it was found helpful to refer to five particular highlands by more
specific names. These have been referred to by the names of cities
located on them as follows: the Lake Wales Ridge, the Winter
Haven Ridge, the Lakeland Ridge, the Brooksville Ridge, and the
Orlando Ridge:
10 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
The Lake Wales Ridge: This ridge is a long narrow highland
which extends some 85 miles in a southeasterly direction from
the vicinity of the common corner of Polk, Osceola, Orange and
Lake counties at the northwest to a point a few miles north of
Venus in southern Highlands County at the southeast. At most
places it rises abruptly from the flatter lowlands which surround it.
It reaches maximal elevations of about 300 feet near the city of
Lake Wales, but its surface is quite irregular offering considerable
local relief which seems to be the result of three discrete influences;
solution by ground water, stream erosion, and the building of sand
dunes by wind deposition. Without doubt, Pleistocene terrace
deposits are present on some of the lower parts of the Lake Wales
Ridge but most of it seems to be capped with remnants of a fluvial
blanket of bar plain deposits which Vernon (personal communi-
cation) refers to the Miocene and calls "Hawthorn Delta". On
earlier maps, these have been called "Citronelle". (See also Bishop,
1956). The following towns are located along the crest of the
Lake Wales Ridge: Haines City, Lake Wales, Babson Park,
Frostproof, Avon Park and Sebring.
The Winter Haven and Lakeland Ridges: These ridges appear
to the west of the Lake Wales Ridge. Neither of them is as long
or as high as the Lake Wales Ridge, but they seem to bear the same
relation to the lowlands surrounding them. The Winter Haven and
Lakeland ridges terminate rather abruptly at their northern ends,
where the insoluble Miocene beds that support them have been
truncated by erosion. The Lake Wales Ridge, however, does not
leave the area of outcrop of Miocene beds and extends considerably
farther to the north where it dies out more gradually than the
others.
All three of these ridges would be part of Cooke's Central
Highlands. The Lake Wales Ridge, at least, and possibly the
Winter Haven Ridge as well, would be part of Vernon's Delta Plain
Highlands (Hawthorn Delta). The Lakeland Ridge would probably
be included in Vernon's Tertiary Highlands.
The Brooksville Ridge: This ridge is the Coharie-Okefenokee
Sand Ridge of Vernon in its northern part. Toward the south
where Tertiary rocks crop out and Pleistocene terrace deposits
are not appreciably thick, Vernon classified it as Tertiary
Highlands.
The Orlando Ridge: This term is applied to the broad highland
which extends southward from the vicinity of Alachua County
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 11
across the eastern parts of Marion and Lake counties into Orange
County. It would all come under Cooke's Central Highlands, and
most of it would probably also qualify as Vernon's Delta Plain
Highlands.
DRAINAGE OF THE FLORIDA PENINSULA
Eastern Florida differs from other parts of the Atlantic Coastal
Plain in its peninsular character. Throughout much of Pleistocene
time it has changed its size without losing the essential
characteristics of its peninsular form. Little late deformation is
evident and the peninsula seems to have changed its outline
principally by fluctuations in the level of the sea, although sub-
sidence or sagging caused by solution of limestones may have been
a minor factor. At times of high sea level the peninsula was
shortened and narrowed, and at times of low sea level it was
lengthened and broadened. Its maximum length is limited by
profound oceanic depths immediately off the present southern
and southeastern shores. Therefore, it has never been able to
extend much beyond its present shores in these directions.
Elsewhere, however, the present peninsula is surrounded by a broad
area of shallow water, the bottom of which has emerged to widen
the peninsula at times of low sea level. There have been other
times when all that remained above water were narrow elongate
islands. This history has effectively prevented the present entry
of any mainland drainage into peninsular Florida. There are no
extended consequent streams coming into this area from the old
land or Piedmont to the north or west as is so characteristic of the
rest of the Coastal Plain province.
The major surface streams of peninsular Florida flow parallel
with the coasts throughout most of their length. Thus the St. Johns
River flows northward parallel with the East Coast for some 200
miles. Its principal tributary, the Oklawaha, flows parallel with it
throughout the greater part of its length, then turns eastward in
a right angle bend to join the St. Johns. Farther west, the
Withlacoochee River follows a similar northward course throughout
its longest reach. Opposed to these northward flowing streams are
the principal southward flowing ones, the Peace River on the west
side of the Lake Wales Ridge and the Kissimmee River on the east
side. If one considers the southward drift of natural drainage
from Lake Okeechobee to Cape Sable and Florida Bay as a
continuation of the Kissimmee River, then these opposed northward
and southward flowing coast-parallel streams provide the surface
12 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
drainage of nearly the entire peninsula from Jacksonville to Cape
Sable, a total distance of some 350 miles. The only significant
exceptions to this generalization are the short coast-perpendicular
streams of the Gulf Coast and the extreme northwestern part
of the peninsula where the Suwannee River with its principal
tributary, the Santa Fe, dominates the drainage. However, even
these share a coast-parallel trend for some 50 miles.
The fact that these major peninsular streams all flow parallel
with the coast rather than perpendicular to it is of considerable
interest. It is quite the opposite of what one would expect in view
of the movement of artesian ground water in the same region.
In the peninsula most of the bedrock is Tertiary limestone
and solution has apparently opened a widespread system of
anastomosing avenues which permit ground water to flow in any
direction dictated by pressure differential. The piezometric surface
of this water is highest under the highest land, and, in broad
generality, this is along the axis of the peninsula. Hence artesian
flow is generally from central areas to coastal areas. This fact is
attested by the many great springs in the low areas near the coast.
Such a situation would seem to be ideally arranged for the
perpetration of multiple stream captures whereby surface streams
flowing long distances parallel with the coast would be led off
along steeper subterranean routes flowing directly to the
sea by using the proper components of the universal system of
anastomosing solution openings in the bedrock.
Any of innumerable solution widened openings which these
long streams must cross could lead them into such underground
avenues. Yet they maintain their integrity as coast-parallel
surface streams for great distances and reach the sea without
breaking the continuity of their surface discharge. This ability
to resist partition by underground capture no doubt results from
the fact that their valley floors are commonly below the piezometric
surface.
The north-flowing streams, the Withlacoochee, Oklawaha and
St. Johns rivers, flow along topographic troughs surrounded by
higher terraces. The upland surface is everywhere blanketed
with a layer of highly permeable marine sand and is usually
separated from the porus limestone of the artesian aquifer by
impervious sediments. A local ground-water surface is present
in the divide areas and recharge to the artesian limestone is
prevented by higher pressures except for the Withlacoochee
system. Here the openings in the artesian system of limestone
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 13
aquifer are apparently not adequate to discharge all the water
which infiltrates into the overlying sand. Hence a high water table
is generally present and the troughs between the higher terraces
become areas of recharge refusal or even artesian discharge and
are able to maintain surface streams.
The area drained by the Oklawaha and the Withlacoochee
rivers is the great topographic saddle between the northern and
southern highlands. In this saddle are located many of the great
artesian springs such as the famous Silver Springs of Marion
County, Fenney and Panasoffkee springs of Sumter County, and
Bugg and Messant springs of Lake County. The presence of these
great springs expresses dramatically the reason why the rivers
can resist underground capture.
There may be a possibility that these large north-flowing
streams are subsequent but it seems small. They flow essentially
parallel with the strike of the bedrock as determined by the flank
of the Ocala uplift, but the Oklawaha rises in a zone of relict
beach ridges which is one of the most prominent of the peninsula.
These can be seen on the photo index sheets of Orange, Lake and
Polk counties (fig.l) and are described in some detail in the section
of this report entitled: "Relict Beach Ridges as Index to Sea Level
Change and Subsidence." The general trend of the Oklawaha is
parallel with the length of these old beach ridges, and it would be
very difficult to think of it as being subsequent to structures which
they have covered ever since this area last emerged from the sea.
Since the river follows the trend of these beach ridges through
the area they cover, it would seem unavoidable to conclude that
it was originally consequent to a trough between adjacent ridges
of this group. Nonetheless, the course of the Oklawaha seems to
have been altered extensively from its original route by the solution
which has caused it to thread through a long chain of lakes. This
chain includes the large lakes, Griffin, Eustis and Harris, toward
its lower end as well as Lake Betsy and Lake Louisa at its head
and several smaller lakes between.
One of the most surprising things about the continuity of these
long coast-parallel streams is the fact that they appear to have
successfully resisted dismemberment by underground drainage
during the glacial stages when sea level was hundreds of feet
below its present elevation. It is, of course, possible that they
were dismembered by subterranean drainage at such times and
reintegrated later. However, the writer does not know of any
evidence to support such a conclusion, whereas there is excellent
14 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
evidence that parts of the present streams incised their valleys
to depths considerably below their present levels during these
glacial stages of lowered sea level. Drilling done during exploration
of the route for a cross-peninsular canal, proposed some years ago,
revealed sedimentary fill in the order of 100 feet in thickness in
the valleys of the St. Johns River, the Oklawaha River, Orange
Creek and the Withlacoochee River. The presence of these deeper
ancestral valleys beneath the floors of the present ones occupied by
the same streams suggests that surface streams in this region
ivere not dismembered by lowered sea levels which in turn suggests
that the piezometric surface was not greatly affected by them
either.
There is evidence for the lowering of the piezometric surface
in the northern peninsula (see section of this report on the relation
of lakes to piezometric surface), but it would seem that this must
have resulted from some influence other than a lowered sea level.
Possibly it has resulted merely from the maturation of the
peninsular karst with accompanying increase in the number, size
and continuity of solution openings available for subterranean
drainage.
It would seem plausible that sea level lowering alone should
have little effect upon either the piezometric surface or the water
table for it would merely extend the land area broadly seaward at
essentially the same slope as that possessed by the present land
area. Only at the southeast, south of Palm Beach, would emergence
bring forth appreciably steeper slopes than those now exposed.
With increasing subaerial exposure of the continental shelf,
fewer and smaller solution openings should be encountered because
the lower the surface the less should be the number of times and
the total length of time that it has been emergent and exposed to
subaerial conditions. Thus periods when the present continental
shelf was subject to solution by circulating fresh ground water
should have been infrequent, short-lived and limited to the glacial
stages when sea level was low. In contrast, during interglacial
stages of warmer weather sea levels were higher and solution
was probably arrested in these lower areas because the openings
were largely filled with sediments and salt water which had little
capacity to dissolve limestone.
According to this idea, coastal-plain karst should be most mature
on the highest land surfaces. Examination of such high areas as
the Lake Wales Ridge seems to confirm this idea, for it is blanketed
with insoluble rocks of rather low permeability (Hawthorn Delta)
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 15
yet no single part of its surface is free of the basins produced by
solution of the underlying limestone.
Also, in line with what has been said above, this probable
paucity of solution openings in the less frequently emergent lower
surfaces should militate against lowering of the piezometric surface
in the higher areas as a result of sea level drop.
Differences of climate produced by changes from glacial to
interglacial stages as well as other causes might affect ground-
water levels through their effect on rainfall and evaporation.
Another possible factor that would work toward elevating or
retaining the piezometric surface and the water table is the filling
of the cavernous solution openings with sediment during periods of
submergence. Although this should have little effect upon the water
level in the previously emergent areas, after sea level lowering
the newly emergent areas might well have higher water levels
than they did before submergence.
Thus the plugging of subterranean drainage avenues by
sedimentary fill would in some measure undo the work of the
presubmergence karst cycle. With prolonged re-emergence the
reactivation of the karst cycle would slowly open new avenues of
underground discharge and the piezometric surface and water table
would gradually drop.
Perhaps it is not implausible that this process accounts for the
drop in the piezometric surface which seems to have occurred in
the northern peninsula where disappearing lakes, dismembered
rivers, and abandoned spring heads all suggest such a drop.
These evidences of a lowered piezometric surface all appear
in a part of the peninsula which is included in the higher terraces
and therefore should have had a longer period of emergence through
which the reactivated karst cycle could operate to reopen old
subterranean avenues of drainage and create new ones.
Vernon (1951) refers to an old abandoned coast-parallel valley
which extends in a north-south direction across Gilchrist and
northern Levy counties. This may mark the course of a former
coast-parallel consequent stream which has been dismembered
by underground capture assisted by a falling piezometric surface.
It well may be that it would be reoccupied by a coast-parallel
stream if the piezometric surface should rise to the level of its
floor.
Although it is difficult to specify the details of such captures
as Vernon suggests, odd bits of evidence support their reality.
Thus it is a significant fact that there are no coast-parallel streams
16 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
in regions where the valley floors are above the piezometric surface.
Yet coast-parallel streams are dominant in areas where the
piezometric surface is higher than the valley floors.
Again, in the great coastal re-entrant which forms the northern
third of the Gulf Coast of the peninsula, it is a paradoxical fact
that the large streams, the Withlacoochee and the Suwannee, both
debouch at the apices of minor salients in the coastline; whereas,
the smaller streams, the Waccasassa and the Steinhatchee, both
reach the coast at the heads of bays, Waccasassa Bay in the case
of the Waccasassa River, and Deadman's Bay in the case of the
Steinhatchee.
Considering the discrepancy between the great length of the
Withlacoochee and the Suwannee rivers on the one hand, and the
shortness of the Waccasassa and Steinhatchee rivers on the other,
it would seem probable that the Waccasassa and Steinhatchee
rivers were once outlets for much larger drainage areas than
they now possess. Complementarily, the lower reaches of the
Withlacoochee and Suwannee rivers would seem to have escaped
from the former, longer routes (probably coast-parallel) via the
valleys of what once were minor coast-perpendicular streams.
In this connection it would also seem significant that the large
streams, both the Suwannee and the Withlacoochee, flow over
essentially bare limestone throughout the lower parts of their
courses. Whereas, the Waccasassa, at least drains a broad area of
delta plain (Vernon, 1951) which extends nearly to its headwaters,
and under which the limestone is buried by a thin layer of fluvial
sediments.
Perhaps it should be mentioned that Cooke (1939, p. 32) noted
the absence of any estuary at the mouth of the Suwannee River
and suggested that none was present because the river followed a
subterranean course during periods of low sea level.
The voluminous drift of sand southward along the beaches
of the Atlantic Coast has had a significant effect upon the drainage
pattern of all those streams which lie east of the highest peninsular
divides. As stated in the section of this report which describes the
zones in which the larger peninsular lakes occur, all the old beach
ridges that lie east of the Brooksville Ridge and the Lakeland
Ridge seem to have been deposited on Atlantic, rather than
Gulf of Mexico, shores. These beach ridges are very noticeable
features throughout much of this area and, one way or another,
seem to have localized long coast-parallel streams such as the St.
Johns, Oklawaha and Withlacoochee rivers. These streams have
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 17
no counterparts on the west side of the Brooksville Ridge-Lakeland
Ridge axis. There the streams are shorter, more numerous, and
flow more directly toward the coast (see pl. 1). Such coast-
perpendicular consequent streams are essentially absent from the
area east of the major divide. They seem to have been able to
develop on the west side because the land surface there developed
essentially by simple emergence of the sea bottom without the
interposition of constructional features such as offshore bars or
progradational beach ridges. This simple conversion of sea bottom
to land surface without the interjection of drainage-controlling
shore features was made possible by the dearth of beach sand on
the Gulf Coast as compared with its voluminous presence on the
Atlantic Coast.
It will be noted ilso that the zone of large lakes lies in the zone
of coast-parallel consequent streams east of the Brooksville Ridge
and the Lakeland Ridge. In contrast, the zone of coast-perpendicular
streams west of these ridges has no large lakes.
TRENCHING AND DROWNING OF COAST-PARALLEL
STREAMS
Most of the great coast-parallel valleys of the Florida Peninsula
seem initially to have been long narrow lagoons, bays or sounds
behind offshore bars. They probably resembled the present Indian
River and similar lagoons which closely parallel the present east
coast of Florida throughout most of its length. Such elongate
embayments have existed at a number of different levels of sea
[a fact which is graphically shown on MacNeil's (1949) map of the
marine terraces of Florida] and the complexity of their subsequent
history usually increases with their age. They may have been
drained of sea water, occupied and trenched by rivers, inundated
again and filled with sediment during another interglacial stage of
high sea level, and if the divide on the seaward side of the valley
was not submerged they may again have become elongate lagoons or
sounds and the cycle may have repeated itself. However, there is
little compulsion that they should ever have become a stream valley
again if they were inundated and filled with sediment to the level
of the surrounding terrain; for re-emergence following complete
submergence should beget new consequent streams unrelated to
former ones.
Opinions concerning old marine shorelines and terrace levels
in this region are many and varied. A widely held idea (Cooke,
18 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
1945) suggests not only that the higher the terrace the older it is,
but that the terrace flight has been made by a diminishing
fluctuation of sea level in which no single rise crested as high as
its immediate predecessor. Regardless of one's attitude toward
such a specific view of the chronologic sequence in the forming
of these terraces, one can scarcely avoid the belief that each
successively lower terrace is younger than those above it. For
any terrace to be older than a higher one it would have to survive
transgression by the shoreline with all the attendant destructive
forces of beach erosion and longshore sedimentation.
If this idea is correct no incised valley cut by a stream in a
former lagoon on one of the presently preserved terraces during
low glacial stands of the sea, should ever have been occulted by
marine sedimentary fill, for no later sea level reached as high as
the surface on which the engendering lagoon was formed. However,
a valley trenched by a stream during a glacial stage of low sea level
might be partially filled with water and become an estuary during
the ensuing interglacial interval of high sea level. And the estuary
could be filled with sediment up to the level of its water surface,
and a fluvial plain developed up the valley.
Depending upon the depth to which the stream incised its valley
each time sea level dropped, this process of partial drowning
might take place repeatedly at successively lower sea levels. Thus
the lower reaches, at least, of most of the larger streams should
have been trenched during glacial stages of low sea level and filled
with sediment during later interglacial inundations, and this
process should have been repeated for each successively lower
terrace.
Definite evidence of such erosion and fill is limited to a few places
where drilling has fortuitously penetrated the fill and revealed
its presence, not only by its sedimentologic character, but also by
atypical depth to bedrock. In Florida such evidence is found in the
exploratory borings made for the now abandoned cross-peninsular
"Florida Ship Canal" project. These were made along the lower
coast-perpendicular segment of the Withlacoochee River on the
west coast, and on the east coast they were made along the lower
St. Johns River, and the lower part of its principal tributary, the
Oklawaha.
Sellards (1916) and Vernon (1942) describe sedimentary fill in
the Apalachicola and Choctawhatchee rivers which has ponded
the lower reaches of tributary streams.
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 19
THE WITHLACOOCHEE RIVER
The Withlacoochee River in Pasco, Sumter, Citrus and Marion
counties, may have been alternately submergent and emergent
through several cycles with extensive dissection occurring
repetitively during times of emergence and the narrow valleys
thus excavated being partially filled with sediment during times
of submergence. Its valley seems to have been formed originally as
a lagoon behind an offshore bar at the level of the Okefenokee
terrace (150 feet above present sea level) or possibly at the still
higher level of the Coharie terrace (220 feet above present sea
level) isolated remnants of which still exist to seaward (west) of
the Withlacoochee valley (Vernon, 1951) on the Brooksville Ridge.
The present valley floor has elevations of 50 to 80 feet.
That it has been trenched and refilled with sediment is shown,
as Vernon (1951, p. 31; fig. 14) pointed out, by Florida Geological
Survey Well Sample Library No. W-1198 of the investigation for
the formerly proposed route 13-B of the "Florida Ship Canal".
This hole encountered sedimentary fill more than 100 feet thick,
reaching depths as much as 83 feet below present sea level.
However, it would seem that the stream which cut this trench
did not escape from behind the old barrier to the west, the
Brooksville Ridge (Coharie-Okefenokee Sand Ridge of Vernon,
1951) through the same gap which the present Withlacoochee
River uses. For near Dunnellon the present river flows over a
a bedrock lip at an elevation about 100 feet higher than the bottom
of the old sediment-filled valley upstream.
The former route of the stream's escape from behind the
all successive incursions of the sea attained maximum elevations
less than that which produced the stream-engendering lagoon,
there would have been little chance for the stream to escape its
own eroded valley to become superimposed on the undissected up-
land nearby. The only available gap with a floor as low as the pres-
ent broad valley floor of the coast-parallel segment of the Withla-
coochee is the one followed by the Hillsborough River and if the
above described conjecture concerning the relative ages of consecu-
tive terraces is true, then the Withlacoochee must have used this
gap. Thus, it appears that the Withlacoochee has only lately acquired
its present course through the Brooksville Ridge. This assumption
is further supported by Vernon's (1951) observation that the
marine terraces west of the ridge do not turn up the walls of the
Withlacoochee valley, but instead are abruptly cut through by the
valley.
20 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Perhaps the most plausible assumption concerning the earlier
route of the Withlacoochee's escape from behind the ridge is that
it went through the gap now occupied by the Hillsborough River
east of Zephyrhills in Pasco County.
The relationship between the Withlacoochee and Hillsborough
rivers is a very unusual one. They share a common headwater in
the upper Withlacoochee River which flows southwestward out of
northern Polk County to a point near Richland in the southeastern
part of Pasco County. Here the river bifurcates in a downstream
direction. The larger part turns abruptly northwest and continues
to bear the name Withlacoochee. The smaller part continues in
the southwesterly course of the common headwater (upper
Withlacoochee) and is called the Hillsborough River.
At the time of the writer's visit to these two diffluent streams,
the Withlacoochee seemed to be receiving about twice as much
water as the Hillsborough according to a crude estimate of their
discharges made by timing flotsam over an estimated distance to
determine velocity, and determining cross sectional area by
sounding with a pole and measuring the distance from one side of
the stream to the other by pacing across the bridges. Admittedly
subject to the grossest of error, these measurements showed the
Withlacoochee below the point of diffluence to be discharging about
100 cubic feet per second, the Hillsborough a little less than half as
much. These estimates were made toward the end of the summer of
1955, a time of considerable drought.
This diffluence is of a nature markedly different from that
of the distributaries and drainage networks ordinarily met with.
Most of these are found on plains of fluvial aggradation, where
there is virtually no relief. Between such diffluent streams the
interfluves are so flat that individual components of the distribution
system are able to migrate across them easily in answer to any
laterally directed force, or by avulsion. In such cases it is clear
that the diffluence of the streams is the result of their own
aggradation.
In the case of the diffluence of the Withlacoochee and the
Hillsborough there is little evidence of aggradation. The gradient
of the Hillsborough at least is fairly high and the streams seem
to be carrying no suspended load and little bed load. Moreover,
the interfluve between the diffluent streams is the high ground
of the Brooksville Ridge which rises more than 150 feet above
the level of these streams. There is no evidence of a fluvial plain
of aggradation surrounding this ridge as in the case of the delta
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 21
of the Hwang Ho River in China which has built a delta plain
around a coastal highland.
These peculiarities, the low gradient, common headwaters, etc.,
suggest that the coast-parallel segment of the Withlacoochee was
formerly a tributary of the Hillsborough River. It will be noted
from the map (pl. 1) that the Hillsborough River, despite its
lesser discharge, occupies a continuation of the upper Withlacoochee
valley in the same straight line; whereas, the coast-parallel segment
of the Withlacoochee diverges at right angles. This angular
relationship would be a normal one if the coast-parallel segment
of the Withlacoochee flowed into the Hillsborough rather than
away from it. That is, if the juncture of the streams were confluent
rather than diffluent.
It is also unusual that the upper Withlacoochee and the
Hillsborough both share a fairly steep seaward gradient while the
coast-parallel segment of the Withlacoochee, downstream from the
point of diffluence, has very little fall despite the fact that it
receives more than two-thirds of the diffluent water. One would
think that the greater share of the water would follow the shorter
and steeper Hillsborough River.
As shown on the Zephyrhills quadrangle, the Hillsborough
River has a fall of about 5.3 feet per mile between a point about
one mile downstream from State Highway 156 (or Atlantic Coast
Line Railroad) and a point about one mile upstream from the
Seaboard Air Line Railroad (between Zephyrhills and Crystal
Springs). But this map has a 20-foot contour interval and only
two contour lines cross the river on the map, so it is not possible
to determine whether the fall in the river is fairly uniform or
irregular. However, it is about six miles along the axis of the flood
plain of the Hillsborough River from the 60-foot contour line
(the highest one that crosses the Hillsborough River on the
Zephyrhills quadrangle) to the point of diffluence from the
Withlacoochee near Richland, where a profile of the Withlacoochee
(fig. 2) presented by the U. S. Army Corps of Engineers
(unpublished) shows an elevation of 68 feet at normal water
surface. Thus there should be a difference of some eight feet in
the first six miles of the Hillsborough below the point of diffluence,
or an average fall of about 1.3 feet per mile.
The upper reach of the Withlacoochee above Richland has an
average gradient of about 1.5 feet per mile as computed from the
profile (fig. 2). Thus the gradients of these two stream segments
seem to be about equal and compatible with the idea that they are
22 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
parts of a single continuous stream which has occupied this
straight line valley for a long time.
Below the point of diffluence near Richland the Withlacoochee
River has a mean gradient of about 0.7 foot per mile for the first
30 miles, and although this is only half that of the upper
Withlacoochee or the Hillsborough, it flattens still farther in the
next 54 miles (the reach which includes the deviation that takes
it around Lake Tsala Apopka) having a mean gradient of only
0.3 foot per mile.
This flatness of gradient in the Withlacoochee below the point
of diffluence could facilitate reversal of flow and the fact that it
exists argues against the coast-parallel segment of the Withla-
coochee valley floor being a fluvial plain. Rather, the flatness of
profile, the peculiarities of Lake Tsala Apopka (discussed below),
the narrow incised valley at its northern end near Dunnellon,
plus the way the lower Withlacoochee (below the Dunnellon
narrows) cuts sharply across the lower marine terraces, all suggest
that this section of the Withlacoochee valley has a very brief
history as the route of a northwestward-flowing stream.
Vernon (personal communication) has called attention to the
lack of fluvial deposits along the channel and the presence of many
outcrops of the phosphate-rich Alachua formation. These suggest
that there has been no history of valley cutting and fill in the late
development of this part of the Withlacoochee valley.
Further suggestion of this may be had from the fact that the
narrow incised valley through which the Withlacoochee leaves its
long coast-parallel segment is cut into the floor of a gap in the
confining Brooksville Ridge. The floor of this gap offers some
topographic irregularity, but in general its elevation is about the
same as the floor of the broad valley occupied by Lake Tsala
Apopka and Lake Panasoffkee, the coast-parallel segment of the
Withlacoochee River, and the swamps to the northeast of the river.
Nothing was seen on the floor of this gap to suggest that it was
ever a fluvial plain. Rather its topographic appearance resembles
karst. This would suggest that the Withlacoochee owes its present
escape route through the Brooksville Ridge to a newly formed gap
produced by solution, and that it has begun the task of trenching
the floor of this gap thus forming the present narrow channel in
the limestone in the vicinity of Dunnellon.
The writer is inclined to the belief that a large lake occupied
most of the coast-parallel valley before the drainage was reversed.
The presence of such a lake on the high northeastern side of the
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 23
Dunnellon gap would have assisted passage of ground water
through permeable parts of the ridge from northeast to southwest
(or from landward to seaward). This would eventually have
opened a continuous subterranean passage of sufficient cross-
sectional area to drain the lake and facilitate reversal of flow in
the coast-parallel segment of the Withlacoochee River. Vernon
(1951) shows a fault passing through the sand ridge at this point
which also could have facilitated the leakage of ground water from
the high northeastern side to the lower southwestern side. In a
personal communication he has also called the writer's attention
to the peculiar lithologic nature of the Avon Park limestone and
Inglis formation in the vicinity of Dunnellon. These rocks are very
friable, mealy, loosely knit aggregates of dolomitic euhedra, and
are highly permeable, a fact which should facilitate leakage of
lake water through the foundation of the sand ridge. Solution
should also be aided by the fact that the water leaking through the
ridge should have been mostly lake water and therefore more
heavily charged with organic acids than ordinary ground water
would have been.
The former presence of a large lake is suggested by the great
width of the flat floor of the coast-parallel valley to the northeast
of the confining Brooksville Ridge, together with the present
existence of two large and many small lakes all at nearly the same
level and all connected in a common surface drainage system.
Moreover, there are no old meander scrolls, oxbows or braided
channels to suggest that this wide plain had a fluvial origin.
The floor of the long coast-parallel segment of the Withlacoochee
valley is considerably wider in its northwestern part, toward
Dunnellon, than in its southeastern part toward the point of
diffluence. The wider northwestern part of the valley has some 20
feet of local relief encompassed between elevations of 50 to 70 feet.
The narrow southeastern part bears more resemblance to a fluvial
plain and has less local relief. Its elevation is probably about 75
or 80 feet. The normal water surface in the river at its southeastern
end (at the point of diffluence) is about 68 feet. Thus it would
have been possible for a large lake occupying the wider north-
western part of the valley to have drained through the narrower,
southeastern part into the Hillsborough River, without the depth
of the lake being any greater than the norm of large Florida lakes.
The direction of drainage would have been the reverse of the
present direction of flow of the Withlacoochee River.
This ancestral lake, of which Lake Tsala Apopka and Lake
24 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Panasoffkee are remnants, could not have drained northwestward
for the valley ends a short distance northwest of the latitude where
the present Withlacoochee River cuts through the Brooksville
Ridge. A smooth rounded scarp separates the north end of the
valley from high mature karst to the northwest. Rainbow Spring
flows out of the base of this scarp where it intersects the sand
ridge. This spring flowing at a rate of 450 million gallons per day
may have been the head of the ancestral Withlacoochee River
during its lacustrine phase.
A comparison of the valley of the Hillsborough River with that
of the comparable segment of the Withlacoochee, below Dunnellon,
offers some considerable support for the idea that ancestral drain-
age in the coast-parallel segment of the Withlacoochee was via
the Hillsborough River. The valley of the Hillsborough has certain
attributes which suggest that it has been in existence for a long
time; whereas, the lower Withlacoochee has no such attributes.
Thus:
1. The Hillsborough River flows into Tampa Bay, which is the largest
estuary on the west coast of peninsular Florida; whereas, the
Withlacoochee enters the sea abruptly with no embayment at all.
2. The Pamlico terrace turns up the valley walls of the Hillsborough
River, but cuts abruptly across the valley of the Withlacoochee, as
Vernon (1951) has pointed out.
3. The Hillsborough River follows a broad swampy flood plain or
possibly a filled estuary, whereas the Withlacoochee flows in a narrow
channel in limestone bedrock suggesting the initial stage of the
fluvial cycle.
If a former lake had been partially drained to leave a broad
swampy area dotted with smaller lakes, it might explain some of
the pecularities of this area which are not found elsewhere in the
region. Thus, Lake Tsala Apopka is unique among Florida lakes
in being a maize of small interconnected basins which collectively
cover an area some 18 miles long and six miles wide. Moreover,
the Withlacoochee River, which is indistinguishable from the lake
at its southwestern end (Vernon, 1951), nonetheless, manages to
dissociate itself from the lake and describe a considerable loop to
get around it as it flows downstream in a general northwesterly
direction. It seems to the writer that this would be a difficult
situation to explain if the present lake were not the remnant of a
larger one through which the river formerly flowed.
Presented with a new, shorter and lower outlet to the northwest,
the lake drained, save for basins in its bottom, and the river
began to incise its bottom. The remaining parts of the lake over-
flowed into the river, but the river by incising itself below the
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 25
level of the adjacent remnants of the lake, succeeded in draining
into extinction those northern parts of the lake through which it
flowed. Thus the river was separated from the lake along the lake's
eastern and northern shores. Vernon (1951) noted this peculiarity
and observed that the level of the river near the northern edge of
the lake was ordinarily a few feet lower than that of the lake.
It is a matter of interest that no similar multiple-basin lake
appears on the northeast side of the river across from Lake Tsala
Apopka. Instead there are only a few small unconnected lakes. A
difference in the nature of the floor of the large ancestral lake
may possibly account for this, a difference which might be ex-
plained by the fact that the present northwestward course of the
Withlacoochee River closely parallels the traces of several parallel
faults (Vernon, 1951). Perhaps these faults present rock of some-
what different character on the northeast side of the river, rock
which has behaved differently in its reaction to solution. Again
there might be insoluble fill on the northeast side of the river and
soluble limestone on the southwest side. However, a preferable
explanation for the absence of a large Tsala Apopka type lake on
the northeast side of the Withlacoochee is as follows.
The aerial photographs of the valley floor of the coast-parallel
segment of the Withlacoochee valley surrounding Lake Tsala
Apopka show a number of small lakes and many swamps which
together form a pattern very similar to that made by Lake Tsala
Apopka. However, these lakes are small and they are not connected
by open water as are the several parts of Lake Tsala Apopka. This
is because they do not receive sufficient water to allow them to
overflow, one into the other, through avenues of open water. Sup-
plied, as they are, with little more than ground water seepage they
discharge from one to the other unobtrusively through large
swampy areas and do not give the impression of an interconnected
drainage system.
On the other hand, Lake Tsala Apopka occupies a favored place
insofar as voluminous discharge is concerned. It has the high land
of the Brooksville Ridge on its southwest side and the Withla-
coochee River runs around the rest of it. The Withlacoochee can
discharge water directly into its upper or southeastern end, where
river and lake are at the same elevation. But the lake discharges
into the river at its northwestern or downstream end where the
river is lower than the lake. This voluminous discharge of river
water fed through the lake enables it to connect, by narrow bights
of open water, several basins which might otherwise have been
26 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
connected only by swampy woods. Actually, Lake Tsala Apopka is
a chain of lakes rather than an individual lake. Note that there is
a water drop of some five or six feet between the southeast and
northwest ends of the lake. Actually there is nowhere near as
much difference between the conditions in Lake Tsala Apopka and
those on the other side of the river as are suggested by the usual
maps. On the aerial photographs there is not much distinction. In
mapping Lake Tsala Apopka much swampy growth has been
omitted, while on the northeast side of the river many areas over-
grown with aquatic plants are shown as swamps rather than lakes.
And, of course, small scale maps do not ordinarily distinguish
between swamp and dry land although they would show Lake
Tsala Apopka as a large integrated lake of open water.
Stubbs (1940) observed that in the vicinity of Lake Tsala
Apopka the piezometric surface is higher than the valley floor and
suggested that the river is fed by springs in its bottom. Dr. Robert
O. Vernon has informed the writer that there are many artesian
springs along the Panasoffkee channel. Perhaps the lake receives
artesian water in similar fashion. In this connection, it may be
worth mentioning that it occupies a position similar to that of the
nearby Rainbow Spring. Both are located at the eastern foot of
the Brooksville Ridge, and in the area of outcrop of the Williston
and Inglis formations, while most of the valley floor on the north-
east side of the river lies outside the area of outcrop of these
formations.
Why the Withlacoochee and Hillsborough rivers have maintained
such unusual and seemingly precarious diffluence is a difficult
question to answer. It may be that neither of the two streams is
in a degrading condition and therefore neither can attain any
advantage over the other. Both streams flow on broad
plains with neither meander swing terraces or levees. This
suggests that neither is actively aggrading or degrading, and
therefore neither has control of any mechanism which might
enable it to divest itself of the other, unless it be the cumulative
growth of organic matter coupled with the flotsam it traps.
Discharge from the Withlacoochee River into the Hillsborough
may be intermittent, for a report on the Withlacoochee by the U.S.
Army Corps of Engineers (unpublished) makes the following
statement:
"At a point about 130 miles above the mouth, near Richland, there is
a flat swamp area, with elevations about 70 to 80 feet, densely wooded
in part, between Withlacoochee River and Hillsborough River. The
distance between these rivers at this point is 31/2 miles. During flood
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 27
stages of Withlacoochee River water overflows this area for a width
of about one mile and empties into the Hillsborough River."
Again, in a report on the Hillsborough River, the Corps of
Engineers state:
"It is estimated that a flow of about 3,500 cubic feet per second passed
over the divide (italics, the present writer's) from Withlacoochee River
to Hillsborough River during the 1934 floods."
Neither of these reports notes any diffluence below flood stage
and the Withlacoochee report describes the location of the head of
the Hillsborough River as three and one-half miles from the
channel of the Withlacoochee. Yet in the summer of 1955, a time
when water levels were notably low throughout Florida, the writer
estimated a discharge of some 500 cubic feet per second passing
under the Hillsborough River bridge on U.S. Highway 98 at a
distance of no more than one mile from the channel of the
Withlacoochee.
The channel of the Hillsborough River at U.S. Highway 98
may well be artificially accentuated for the water emerges from
and passes into the cypress swamp above and below the bridge.
It may well be that there was little, if any, recognizable channel
in this part of the Hillsborough River at the time the Corps of
Engineers made their surveys, for U.S. Highway 98 has very
recently been built across the fluvial plain on a continuous fill which
offers only one bridge opening as a means of escape for water which
may formerly have discharged as a disseminated flow through
swampy forest.
However, there must have been some recognizable channel
through the swamp for the planimetric map of Pasco County (fig.
3) shows a continuous channel from the Withlacoochee River to
the Hillsborough River; and the aerial photographs (fig. 4) also
show a sinuous avenue through the flood plain forest which suggests
a connected channel.
DRAINAGE OF THE AREA BETWEEN THE ST. JOHNS
AND KISSIMMEE RIVERS
In this area between the St. Johns River (or St. Johns swamp)
and the Kissimmee River the drainage is essentially consequent to
an emergent marine surface. The divide runs essentially parallel
with the present Atlantic Coast and with the St. Johns River. It
maintains a crest elevation approximating 70 feet for about 125
28 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
R-Z3-FE
I
H- -iLSi-OUGH -OUNTY
HI LLSBOROUG H COUNTY
A PLANIMETRIC MAP SHOWING
DIFFLUENCE OF WITHLACOOCHEE
AND HILLSBOROUGH RIVERS
Figure 3
Figure 4
Aerial photograph of area in southeastern Pasco County showing diffluence of
Withlacoochee and Hillsborough rivers.
30 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
miles between the vicinity of Lake Hart at the north and the
latitude of a line joining Vero Beach with Lake Istokpoga at the
south.
In the east-west cross section, this divide, an elongate swell,
slopes gently in both directions from a high which is slightly
nearer its western than its eastern edge. At the Pamlico scarp on
the east, the slope steepens abruptly, descending from an elevation
of about 50 feet at the crest of the scarp to about 20 feet at its
foot, or 15 feet at the level of the swamp along the St. Johns
River.
At the west the slope steepens in similar abrupt fashion where
it descends to the alluvial plain of the Kissimmee River. There,
however, the descent is not as great because the alluvial plain of
the Kissimmee is higher than that of the St. Johns.
Because of the asymmetric location of the divide, the east-
flowing streams are considerably longer than the west-flowing
ones. The drainage map (pl. 2) shows this, as well as the essential
Plate 2
LEGEND
SWAMP (AREAS ARE SOMEWHAT SIMPLIFIED IN OUTLINE
AND CERTIAN ARIAS OF SWAMP LAND WITHOUT
SURFACE DRAINAGE CONNECTION HAVE BEEN LEFT
OUT )
KI-- SSIMME RIVER--ST JOHNS RIVER DIVIDE
(NOTE THAT IT IS IN UPLAND SWAMPS IN THE
SOUTHERN F ART OF THE MAP.)
M BASE OF PAMLICO SCARP
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 31
opposition of the St. Johns tributaries to those of the Kissimmee.
It may be noted that the former tend to have main streams which
flow directly down the lower part of the Pamlico scarp. These
usually bifurcate near the crest of the scarp, the two tributaries
extending in opposite directions along the same straight line, at
right angles to the main stream and parallel with the length of the
scarp. These opposed tributaries appear to be consequent to the
shallow troughs of former narrow lagoons behind offshore bars or
swales between beach ridges. Such bifurcations can be readily
seen in Fort Drum Creek, Blue Cypress Creek, and Jane Green
Creek. In Pennywash, Wolfe, Cox and Taylor creeks farther to the
north, the tendency for lineation of the tributaries parallel with
the Pamlico scarp is present but less pronounced.
It would seem most plausible that the bars were formed along
the seaward edge of the broad plateau-like area between the St.
Johns and Kissimmee river valleys at a time when a former high
sea level had lowered sufficiently to expose the edge of this marine
depositional plain to the effects of wave action and bar building.
Extending westward from these coast-parallel stream reaches
there are usually a number of tributaries which flow essentially
eastward but with numerous rectangular jogs where they seem
to have been consequent to the troughs between parallel bars of
progradation or multiple beach ridges. Some of these bars as well
as the headwater tributaries controlled by them can be seen in the
aerial photograph shown in figure 5.
The Kissimmee River tributaries, on the west side of the divide,
are shorter and less geometric in pattern. They also have a more
normal angle of confluence with the axial trunk of the Kissimmee
itself, flowing generally throughout their length in courses which
make an acute angle with the valley of the main stream. This
is in marked contrast to the relation between the St. Johns River
and its east-flowing tributaries, which characteristically enter the
main valley at right angles.
These contrasting patterns suggest that the tributaries of the
St. Johns River are consequent to coastal features produced by a
shore which was open to the Atlantic Ocean, while the tributaries
of the Kissimmee River are consequent to the floor of a protected
bay.
The topographic effects of solution are evident generally
throughout the area between the St. Johns and Kissimmee rivers,
but they have increasing effect upon the drainage toward the crest
of the swell in the divide areas near the Kissimmee valley, rather
than near the Pamlico scarp. Generally throughout the eastern
32 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Figure 5
Aerial photographs of part of Osceola County showing beach ridges.
half of the area the surface drainage maintains its integrity very
well and shows few discrepancies of pattern which might suggest
that solution had diverted it from its original consequent course.
The sharp topographic break of the Pamlico scarp has provided
enough fall to allow the east-flowing streams to cut recognizable
valleys, but the westward slope from the main divide to the
Kissimmee River has less than half as much fall and is more uni-
formly gentle in gradient.
In the headwaters the surface drainage is poor and there is a
strong tendency for networks of swamps to cap the divide area. To
the east, these drain into the definitive ramifying St. Johns River
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 33
tributaries, but to the west, dubiety of direction of flow and multiple
outlets for swamps are the expression of original irregularities in a
marine surface modified by solution of underlying carbonate rocks.
It is evident that in this flat swampy divide area the water table (at
least at times of wet weather) is very near the surface. Thus with
both piezometric surface and water table high this is probably an
area of frequent recharge refusal, and solution by near surface
lateral discharge could be a significant process in producing these
indeterminate drainage ways, swampy draws and shallow lakes.
At any rate, it is obvious that this drainage is in its first cycle,
because of its lack of incision and its consequent relation to the
relict beach ridges. The bottoms of the swales are too close to the
crests of the swells to allow any possibility of the subterranean
capture cycle. It is the writer's impression that these streams
have courses which are essentially consequent but modified either
by differential solution of the rock surfaces over which they flow,
or by a simple sagging of these surfaces as a result of solution
within the rock that underlies them. However, the last of these
two possibilities would seem less plausible because the drainage
pattern of the surface streams shows little indication of structural
control or subsequence.
RELICT BEACH RIDGES AS INDEX TO SEA LEVEL
CHANGE AND SUBSIDENCE
Continuous beach ridges are among the most sensitive indicators
of former sea levels. Built originally at the very edge of the sea
they should remain level if there has been no movement in the
region which supports them. Thus if peninsular Florida has
suffered no late deformation and present sea level is lower than
several Pleistocene maxima, the relict beach ridges preserved from
these former maximal sea levels, except for dunes, should still be
level along their length, though presently found at inland locations
and at elevations well above present sea levels. On the other hand, if
such relict beach ridges vary in elevation along their lengths, this
should be evidence for movement either by tectonic action or
through subsidence produced by solution in underlying limestones.
Considering the great amount of evidence for voluminous removal
of limestone by solution throughout the peninsula, it would seem
most plausible that such ridges, or at least the older and higher of
them, should have suffered differential sagging or subsidence along
their lengths.
An examination of relict beach ridges throughout the central
34 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
peninsula made with this problem in mind seems to show some
considerable differential subsidence of the higher ridges but little,
if any, in the lower ones.
Relict Beach Ridges in Osceola and Orange Counties: A zone
of relict beach ridges which appear along the divide between the
St. Johns and Kissimmee rivers (fig. 5) shows little evidence of
subsidence caused by solution. These ridges extend some 55 miles
from the vicinity of Kenansville, Osceola County, to the area east
of Orlando, Orange County. Throughout this distance the height
of a given ridge varies little, those along the western edge of the
zone center around crest levels of 75 to 85 feet above present sea
level. North of Lake Hart, in the area east of Orlando, there are
more crest levels reaching elevations of 85 feet than there are
farther south, but the discrepancy does not seem greater than that
which might be accounted for as differences in the original height
of the ridges.
As seen on the aerial photographs of Orange and Osceola
counties, these ridges cover a triangular area which narrows acutely
to a point at its southern end near Kenansville, and widens north-
ward to become a zone some 16 miles across east of Orlando.
The western part of this triangular area seems to be composed
of progradational beach ridges built at a fairly static sea level, for
the elevations of ridge crests vary little throughout its length or
breadth. Furthermore, the several ridges which compose this
western part of the triangle, converge and diverge along their
length, suggesting the oscillation between progradation and beach
erosion which might be expected during a period of stable sea level
along a coast swept by vigorous longshore currents, beaten by large
waves, and generously supplied with sand.
The relict beach ridges of the eastern part of the triangle are
quite different from those of the western part. On the aerial
photographs they are seen to be mutually parallel (fig. 5). Adjacent
ridges show no tendency either to coalesce or diverge along their
length. Instead, each individual ridge remains discrete from its
neighbors though they all lie parallel with each other. This
meticulous preservation of the identity of the individual ridges
suggests that they were formed by a sea whose level was falling
rather rapidly. The regression of the sea across a very gently
inclined surface would have caused the shoreline to move seaward
at a rate which forstalled effective beach erosion and permitted a
succession of beach ridges to form at successively lower levels so
that they could not run together along their length. This suggestion
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 35
is borne out by the data obtained from the topographic maps, which
show that the ridges of this eastern part of the triangular area
are successively lower to the east, dropping more or less regularly
from the 75 to 85-foot elevations of the western part of the triangle
to the crest level of the Pamlico scarp, or the top of the valley wall
of the St. Johns River on the east, at elevations in the neighborhood
of 50 feet.
The significance of this triangular zone of beach ridges is dis-
cussed further in the section of this report entitled "The Cross-
Peninsular Divide."
Relict Beach Ridges in Polk and Lakl Counties: A series of
beach ridges which are considerably higher than those of Orange
and Osceola counties are found farther west, extending more or less
along the axis of the peninsula in Polk and Lake counties. The
most southerly place at which they can be picked out on the aerial
photographs is the area around Winter Haven, reaching from the
Lake Wales Ridge to the city of Bartow. This distance, 18 to 20
miles, is representative of the width of the zone in its southern part.
It is difficult to know whether the Lake Wales Ridge itself should
be included in this zone, but several considerations suggest that it
should.
These relict ridges are seen best on the assembled county photo
index sheets (fig. 1) for they are rather difficult to discern over
short distances.
At the north in the latitude of Lake Griffin, in northwestern
Lake County they become too inscrutable to follow. However, there
is no indication that the original ridges ended there, and there
seems to be a good possibility that they once extended farther to
the north, but have now been destroyed, or masked, by later events.
The width of the zone, as far north as it is fairly easily recognizable,
is about commensurate with its width at the southern end.
Unlike the beach ridges of Orange and Osceola counties, which
have crests at fairly uniform elevation throughout their length,
these higher relict ridges are quite variable in elevation. They
form a region of considerable local relief, although it would seem
probable that they originally had as little surface irregularity as
those of the lower zones farther east. Only a small part of the
area covered by these ridges has been mapped topographically,
and the writer cannot speak with certainty of the range in
elevation of the ridge crests. However, along individual ridges,
crest levels will be at least as high as 180 feet and possibly as low
as 80 feet.
36 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Such wide and erratic variations in the elevation of features
which must have been made very close to a former sea level can
only suggest that they have been reduced in stature by some
denudational agent. Apparently they have been reduced by solution
of the underlying limestones. By this mechanism they have
subsided, or sagged, differentially without loss of their planimetric
characteristics. Composed essentially of insoluble and highly
permeable sand, they have resisted both solution and erosion and
to a considerable extent have maintained their identity as sandy
ridges which can be picked out on the aerial photographs by their
lighter color and better drainage.
Little evidence of surface erosion can be seen on the aerial
photographs. The ridges are rarely crossed by continuous stream
courses, but the evidence for differential solution is seen everywhere
in the rounded and more or less equidimensional dark areas on the
aerial photographs, which represent swampy or lake-filled solution
depressions.
There is a recognizable change in the appearance of these
beach ridges where they cross the north-facing scarp at the
northern edge of the highland marked by the Lake Wales, Winter
Haven and Lakeland areas. This scarp is seen easily at Polk City,
which is situated on its crest. To the north it overlooks the low-
land from which the Miocene rocks have been eroded. Despite this
change in appearance, there is an unbroken continuity of the
lineation across the scarp and up onto the highland to the south,
as well as across the lowland to the north. The individual ridges
maintain the same width and direction and there is no notable
change in the width of the zone. The only distinction seems to be
in the clarity with which they can be picked out on the aerial
photographs. This seems to be partly a matter of the extent of
solution they have undergone, and partly a matter of the type of
material that appears between them. Thus the soils developed on
the Miocene and Hawthorn Delta sediments generally photograph
a lighter shade than those developed on the older rocks. However,
this may be a result of better drainage. At any rate, the ridges are
best seen where they seem to have been let down the farthest by
solution of underlying early Tertiary limestones and are more
difficultly distinguished where they overlie the sandy sediments of
the Hawthorn Delta, because they themselves are sandy.
As discussed elsewhere in this report, there is good reason to
believe that of all the Florida Peninsula, lowering of the surface
by solution has been most extensive in the area of the Ocala uplift
where the early Tertiary limestones are exposed. Thus the lowering
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 37
of these beach ridges in Lake County would be expected. The
innumerable lakes from which this county gets its name are
themselves a case in point here. MacNeil's map (1949) of the
several Pleistocene terraces shows a distribution of remnants of
the Wicomico and Okefenokee surfaces in the area between
Gainesville and Lake Tsala Apopka (the only part of the early
Tertiary exposure covered by topographic maps). These highlands
are most implausible in plan if they must be explained by any
shoreline process. They are quite obviously the result of a
denudational process and in an area where erosion by surface water
is weak, if not nil, the most plausible conclusion is that they are
high spots of a surface which has been differentially reduced by
solution.
This conclusion poses a serious threat to the validity of terrace
mapping in this area of voluminous solution when it is undertaken
on a basis of elevation alone. From the amount of ground water
discharged through the many great springs of this area of exposed
limestones, it is evident that reduction by solution is not wholly a
surficial affair, but in large measure a matter of subterranean
solution or undermining and the resulting subsidence of the over-
lying surface. If one looks at MacNeil's map with this idea in
mind, the contours shown throughout the area of limestone
exposure seem random and meaningless.
However, new light is shed on the significance of the Lake Wales
Ridge, for this most prominent of the southern ridges falls nicely
into line as an extension of the smoothly curved line of Trail Ridge,
which is the most prominent of the northern relict shoreline
features. One is inclined to conclude that they were 'once
continuous at the level of the Okefenokee terrace, remnants of
which occur in both of them. Both would plausibly have been
protected against the extensive solution-begotten subsidence,
because they are underlain by the insoluble and relatively
impermeable clay-cemented sands of the Hawthorn formation,
"islands" of which appear above the Okefenokee terrace level in
the higher parts of the Lake Wales Ridge. This formation probably
contributed to the sand which made this attenuated sandy island
possible at such a high sea level.
Further speculation based on the subsidence of these relict beach
ridges and the helter-skelter distribution of Okefenokee terrace
remnants shown by MacNeil in the area of exposed limestones
might lead one to suspect that the greater part of this region was
once covered by the Okefenokee terrace, but has suffered differential
subsidence because of solution. It will be noted that the Okefenokee
38 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
terrace of MacNeil which is a long attenuate bar throughout most
of its length on Trail Ridge, broadens at its southern end to cover
a wide triangular area in the vicinity of Gainesville. The base of
this triangle at the south is some 50 miles across from east to
west, and is located essentially at the edge of the area of limestone
exposure. South of the base of the triangle Okefenokee terrace
remnants are found, for the most part, only where there are
insoluble Miocene or Pliocene beds to support them. Possibly the
Okefenokee terrace originally covered the entire area between the
present Trail Ridge at the north, the Brooksville Ridge at the west,
the Orlando Ridge at the east and the Lake Wales, Winter Haven
and Lakeland Ridges at the south.
Oklaiaha Valley: Perhaps it is significant that the coast-parallel
course of the Oklawaha River, from its headwaters in southern
Lake County to its confluence with Orange Creek (a distance of
some 75 miles), is parallel with this zone of high level beach ridges.
It is also immediately west of the projected line which connects
Trail Ridge with the Lake Wales Ridge. Thus it would seem to
have been localized as a consequent stream, draining a lagoon
between adjacent beach ridges of this group.
DUNES ALONG THE EASTERN FOOT OF THE LAKE
WALES RIDGE
Another feature which closely follows the trend of the Lake
Wales Ridge is a marked zone of dunes. These appear consistently
along the foot of the ridge and intermittently along its projected
trend to the north in the saddle between its northern end and the
southern end of Trail Ridge. This zone of dunes is the most
persistent in the peninsula. Beginning at the southern tip of the
Lake Wales Ridge, in Highlands County, it reaches to the northern
end of the Ocala National Forest or the east-west reach of the
Oklawaha River, in northeast Marion County, a distance of some
170 miles. Possibly, it extends even farther to the north, but the
writer has no data beyond the Oklawaha.
These dunes are present along the eastern foot of the Lake
Wales Ridge throughout its length. They are usually worthless
land, covered with palmetto scrub, and they stand out prominently
both in topography and culture from the cultivated areas on the
crest of the Lake Wales Ridge to the west and the flat lowland
plain to the east. The topography of the dune areas (fig. 6, 7, 9; pl.
3) is highly irregular, comprising a maize of rather elongate hills
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 39
separated by depressions which may be either dry, swampy, or
pond-filled. The elevations range from minima of about 50 feet at
the south and 70 feet at the north, to maxima of about 125 to 150
feet. The difference in elevation between the top of a dune and the
bottom of the adjacent depression in rare instances reaches 100
feet, but usually is in the order of magnitude of 20 to 50 feet. In
horizontal dimension the distance from a ridge crest to the center
of the adjacent depression is usually less than 500 feet. It is quite
possible that many of the depressions have been deepened by
solution, either of calcareous, wind-blown sands or of underlying
limestone. The width of the zone varies from less than one mile to
a maximum of about four miles. It wraps itself around the
southern end of the Lake Wales Ridge, forming the conspicuous
scarp which is seen to advantage from U.S. Highway 27, where it
runs off the southern end of the ridge between Childs and Venus,
in Highlands County (fig. 6).
These dunes can be seen very readily on the following topo-
graphic sheets (listed from south to north) : Childs, Lake Placid,
Sebring, Lorida, Lake Arbuckle, Babson Park, Lake Weohyakapka,
Lake Wales, Hesperides, Dundee, Davenport, and Windermere.
Their location is also shown on the map presented here as plate 3.
It is difficult to understand why this particular shoreline should
have produced such a persistent zone of dunes when they do not
seem to be present on most of the other relict shorelines. Even
without an explanation, however, this uniqueness offers
considerable support for the idea that the Lake Wales Ridge was
originally a part of Trail Ridge, for the zone of dunes is
conspicuously present in the place where the northward projection
of the Lake Wales Ridge should be. This is the Ocala National
Forest area of eastern Marion County.
There is much about these dunes which is difficult to explain.
Although most of the dune ridges are curvilinear, there is nonthe-
less a recurrent tendency for them to be elongate in two directions
which are at right angles to each other. The principal trend is
nearly northwest and the secondary one is northeast. These two
trends frequently produce a rectangular pattern in the contour lines
on the topographic maps. This may be seen in the southeastern
corner of the Babson Park sheet and the southwestern corner of
the adjacent Lake Weohyakapka reproduced here as figure 7. The
writer supposes the most facile explanation of this right angled
lineation is to assume that the principal orientation of ridges
(those elongate in a northwest-southeast direction) represents the
development of transverse wind ridges at right angles to the wind
40 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Figure 6
Aerial photographs of southwestern part of Highlands County showing
southeastern end of Lake Wales Ridge and dunes along the east side of the
ridge.
direction. While the other trend, perpendicular to this one, would
represent blowouts and incipient longitudinal wind ridges, elongate
in a direction parallel with the wind.
However, this facile explanation leaves much to be desired when
one notes further that the principal direction of elongation in the
dunes is parallel with the principal set of structural lineaments,
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 41
Figure 7
Part of Babson Park and Lake Weohyakapka sheets showing dual direction
of elongation of dunes.
as manifest in the solution topography to the west, and that the
secondary direction of elongation in the dunes is parallel with the
secondary set of structural lineaments. Of course, it is possible
that by coincidence the effects of wind and structure were parallel,
and it is true that both have a tendency to produce paired perpen-
dicular trends. When the writer first observed this topography he
was somewhat doubtful of its aeolian origin, but a comparison with
known dune areas along the present Atlantic Coast shows much
similarity on the topographic map, even to the same two
42 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Figure 8
Northwestern corner of Jupiter sheet showing dunes formed along present
peninsular east coast.
perpendicular directions of ridge elongation. The present coastal
dunes may be seen to advantage in the northwestern corner of
the Jupiter sheet, reproduced as figure 8.
A part of the Childs sheet is reproduced in figure 9. It shows
a rather characteristic example of the dune country near the
southern end of the Lake Wales Ridge, although the rectangular
pattern is not developed here. This sheet also shows to advantage
the abrupt termination of the dune zone on the east. This is
characteristic of the zone throughout its length along the Lake
Wales Ridge. At its western edge it usually dies out in a less
determinate way, frequently grading into the karst surface of the
crest of the ridge.
The abrupt scarp which persists along the east side of the dune
zone, is obviously a former shoreline, but it lacks the straightness
of the present coastline or the relict beach ridges described above.
Its history in relation to the sea is rather enigmatic, but the
chances are that the irregular line of the scarp results from the
fact that its base is everywhere as low, or lower, than the present
divide between the Kissimmee and St. Johns rivers. Therefore,
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 43
Figure 9
South-central part of Childs sheet showing dune zone and terrace escarpments.
this was probably the western shore of a large embayment which
occupied the present Kissimmee River valley. The dunes may have
been built into the relatively quiet water of this embayment to
form the scarp in question.
On the southern part of the Childs sheet there are two scarps
which coalesce to the north. The lowermost of these has its toe
at an elevation of about 70 feet, and is separated from the toe of
the upper one by a mile-wide terrace flat which is 125 to 150 feet
above present sea level. Since the toe of the upper scarp is 150 feet
high, it is higher than the Kissimmee-St. Johns divide and should
have been open to the Atlantic surf, yet it has the same irregular
plan that the lower scarp shows.
44 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
DRAINAGE OF THE LAKE WALES AND LAKELAND
RIDGES
All the surface drainage of the Lake Wales Ridge flows
southeastward across the ridge to the Kissimmee River system.
The divide is characteristically at the crest of the scarp on the
west side of the ridge, and this scarp is quite different in
appearance from the one at the eastern side of the ridge. It has a
more uniform slope, although a larger drop-off occurs in a shorter
distance, except at the very bottom where there is no change of
slope on the western scarp but a prominent drop on the eastern
scarp. This drop-off at the foot of the eastern scarp results from
the precipitate edge of the dune zone at the toe of the eastern
scarp, which is not found on the west side of the ridge. Moreover,
the low ground to the west of the ridge in the Peace River drainage
is higher by some 25 to 50 feet than that to the east of the ridge
in the Kissimmee drainage.
A very similar situation is found in the Lakeland Ridge,
some 20 to 25 miles west of the Lake Wales Ridge. There, also,
the drainage on the highland seems to be dominantly southeastward,
with headwater divides along the crest of the west-facing scarp on
the west side of the highland. Unfortunately, there are only a few
topographic maps available in this area and this conclusion is
drawn from partial evidence derived from the Bartow and Mulberry
sheets.
Here, as in the Lake Wales Ridge, the drop-off on the western
side of the highland is more precipitate and uniform, while the
eastward descent is more gradual and variant-or even step-like.
Unlike the Lake Wales Ridge, however, no dune zone is present
and there is no abrupt drop-off at the toe of the eastern scarp.
In both the Lake Wales and Lakeland ridges the minor streams
follow courses which vary widely in direction, although in general
they show a tendency to be subsequent to one or the other of the
two principal regional structural lineaments.
The larger streams, however, hold fairly consistently to a
southeastward course. This fact, in association with the fact that
both the Lake Wales and Lakeland Ridges have their divides on
the steeper western side, suggests that there once was a south-
eastward drainage across the entire region in which the ridges
occur. This formerly integrate drainage has been dismembered
and in large measure diverted into the Peace and Alafia river
drainages. Both the Miocene high, which forms the Lakeland
Ridge and the Hawthorn Delta remnant which supports the Lake
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 45
Wales Ridge would plausibly afford enough resistance to solution
to account for the preservation of the relicts of the former drainage
on the two highlands.
On casual inspection, it might appear that the southeast-flowing
streams head at the west-facing scarps simply because these scarps
are retreating and eating away their headwaters. But the fact that
the divide is on the crest of the west-facing scarps of each ridge
and that the drainage direction is the same on the tops of both,
seems good evidence that a former regional southeast-flowing
stream system has been dismembered by the present streams of
the low ground between the highlands. The streams on the tops
of the ridges would be all that remains of the former southeast-
flowing streams. It is possible that they are remnants of the
drainage which formed the Hawthorn delta.
THE CROSS-PENINSULAR DIVIDE
One of the most salient peculiarities of the surface drainage
of the Florida Peninsula is the fact that the major divide does not
follow the length of the peninsula. Instead, it runs across the
peninsula at its widest place, separating north-flowing streams
from south-flowing streams. Thus along a line extending from
Cape Canaveral on the east coast to Indian Rocks on the west
coast, the north-flowing Withlacoochee, Oklawaha and Econlock-
hatchee rivers are separated from the south-flowing Peace Creek
and Kissimmee River. The St. Johns River, which is the longest
north-flowing stream, does not follow this pattern closely in that its
headwaters extend some 25 miles south of this cross-peninsular
zone in which the other streams head. As discussed elsewhere in
this report, the north and south coast-parallel courses of the
major streams are easily explained as being consequent to old
coastal lagoons, such as the present Indian River, or to the troughs
between old beach ridges. However, it is more difficult to explain
the fact that all these coast-parallel streams head along the same
essentially straight cross-peninsular line. If they all flowed on
the same terrace level, this straight divide could be explained by
assuming that an island, elongate in an east-west direction, was
once the only emergent land in the central peninsula and that
coast-parallel streams grew both northward and southward from
it as further emergence or progradation took place.
Such a simple explanation is difficult to accept because the
Withlacoochee, Oklawaha and Peace rivers rise on or above the
level of the Wicomico terrace, while Reedy, Shingle and Boggy
46 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
creeks (the headwater tributaries of the Kissimmee River) and the
Econlockhatchee River all rise on surfaces well below the Wicomico.
Since the Wicomico is one of the best developed and widespread
terraces in peninsular Florida, it would seem fairly certain that
these streams did not all come into being at the same time. There-
fore, it would be necessary to find some factor which could operate
repetitively at successively lower sea levels along the same cross-
peninsular line.
It may be significant in this respect that the present shorelines
(pl. 1) have their most prominent salients at the extremities of this
same cross-peninsular line. At its eastern end is Cape Canaveral,
the first coastal prominence south of Cape Romaine in South
Carolina, some 500 miles to the north. There are no capes to the
south of Cape Canaveral short of the distal end of the coast at
Key West. Somewhat similarly, on the west coast, the most
prominent cape is at Indian Rocks in Pinellas County. The only
other features on the west coast which compare with it as coastal
salients, are Sanibel Island, at the mouth of Charlotte Harbor
and Cape Sable farther south. However, the cape at Indian Rocks
is the most prominent of these from the standpoint of its being
located at the widest part of the peninsula.
Both Cape Canaveral and the cape at Indian Rocks share a
peculiarity which suggests a mechanism for extending the cross-
peninsular divide eastward and westward. They are more or less
integral with the mainland, and their ties with it form the heads
of opposed lagoons which extend long distances along the coast in
opposite directions behind offshore bars. Thus Cape Canaveral
separates the 30 miles of Mosquito Lagoon and Halifax River to
the north from the 100-mile reach of Indian River to the south.
And, in less dramatic fashion, at Indian Rocks on the west coast
the offshore bar approaches so close to the mainland at "The
Narrows" that it all but separates St. Joseph Sound (or
Clearwater Harbor) to the north from Boca Ciega Bay to the
south. Each of these is some 20 miles long, narrowing toward
"The Narrows" at Indian Rocks and widening in bell-mouthed
fashion toward Anclote Key and Tampa Bay respectively.
It would seem safe to say that a lowering of sea level and
withdrawal of the sea from this present coastal situation would
produce four coast-parallel consequent streams diverging north
and south from these two capes, with the headwater divides at
the heads of the present lagoons.
The fact that these two capes which thus seem capable of
producing further drainage divergence are on the same cross-
G E O R G I A
/
LI
L ---- --- r f
*
~ --4
MAP SHOWING THICKNESS -
OF MIOCENE SEDIMENTS
IN RELATION TO LARGE
PENINSULAR LAKES +
(AFTER VERNON 1951) -
SYMBOLS
SISOPACH OF MIOCENE
(Conto.r Intervl: 50 fee1)
4LOLIMITS OF THE HAWTHORN FORMATION
(MARINE FACES)
SCALE IN MILES
Fg 0 r to 10 40
Figure 10
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 47
peninsular line as the major present divide, suggests that some
especial structural or lithologic feature capable of localizing capes
at successive shorelines is present along this line. Among possible
features which might be able to locate capes on successively lower
shorelines, two seem most plausible in this region; first, the
juxtaposition of rocks of different resistance to solution, or erosion
(probably wave erosion) by a fault or zone of faults crossing the
peninsula along the zone in question and, second, the juxtaposition
of such rocks by the beveling and differential dissection of tilted or
flexed strata. There is some considerable evidence that the first
of these features is present along the cross-peninsular divide,
especially near its eastern end, and there is excellent evidence that
the second is present along its central and western parts.
A major zone of deformation crosses the peninsula along the
Cape Canaveral to Indian Rocks axis. It is manifest in the change
in attitude of the Miocene sediments which here begin to dip more
steeply southward. Also minor flexures in the Eocene are parallel
with this axis as shown on Vernon's structure map of the Inglis
formation (Vernon, 1951, pl. 2). On the same map, the Kissimmee
faulted flexure is shown terminating in a fault at its southern end
essentially along this same line inland from Cape Canaveral.
Correlation between these particular features and the cross-
peninsular divide is difficult but it would appear that in its central
and western parts the divide has been localized by the outcrop of
the edge of the Hawthorn formation. Emerging from its
southward dip the Hawthorn is truncated along this line as shown
on the map (fig. 10), which has been adapted from Vernon (1951).
This line of truncation is approximately coextensive with the
northern end of the high ridges in the vicinity of Lake Wales,
Winter Haven, and Lakeland. Likewise, it is essentially the line
along which the deltaic Hawthorn ("Citronelle") and Bone Valley
formations widen abruptly to the south. Vernon's map also shows
a long narrow re-entrant in the line of outcrop of the Hawthorn
formation. This extends northeastward parallel with the cross-
peninsular divide nearly to Lake Hart in south-central Orange
County. It probably represents a breached fold whose axis is a
significant component of the Cape Canaveral-Indian Rocks
structural trend, and the outcrops of the more resistant of the
beveled strata may have helped to localize former capes at times
of higher sea levels when the coast was in this area.
To the north of the cross-peninsular divide the soluble limestones
of the early Tertiary are brought to the surface by the Ocala uplift.
Probably these have long been reduced to topographic levels lower
48 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
than the largely insoluble plastic beds, which form the surface
south of the divide.
Thus the insoluble beds to the south of the divide, truncated at
their northern extremities either by faulting, or beveling and
differential dissection, may have repetitively localized coastal
prominences or capes from which offshore bars, or elongated spits,
extended to the north and south in the manner of the present capes
at Canaveral and Indian Rocks.
For some 25 miles west of Orlando the cross-peninsular divide,
as marked by the heads of the south-flowing Reedy, Shingle and
Boggy creeks (Kissimmee River headwater tributaries) is localized
at the southern edge of the northern and larger part of the outcrop
area of the deltaic Hawthorn formation, which is abruptly narrowed
and offset to the west as it passes southward to its southern
extension in the Lake Wales Ridge area.
It is notable, also, that the high ridges all end abruptly at the
cross-peninsular divide which localizes the southern ends of the
Brooksville and Orlando ridges to the north and the northern
ends of the Lake Wales, Winter Haven, and Lakeland ridges to
the south. One should note, also, that the two northern ridges do
not line up with any of the three southern ones.
From Cape Canaveral to the vicinity of Lake Hart in south-
central Orange County, the writer knows of no salient difference
between the rocks that form the surface north of the
cross-peninsular divide and those which appear to the south of it.
However, it-may be that differences exist, but have been masked
by the thick and continuous veneer of sand which mantles the
bedrock in this vicinity. The fact that some perceptible difference
exists is shown by the peculiarities of the area around Cape
Canaveral.
What seems to be the trace of Vernon's (1951, pl. 2) northeast
striking fault, which truncates the southeastern end of the
Kissimmee faulted flexure can be seen in northern Osceola County.
Apparently the lithologic or structural conditions requisite for
development of large scale solution depressions are presented at
the present surface on the northwest or upthrown fault block. The
trace of the fault seems to follow a nearly straight line marked
by the southeastern edge of the group of large lakes which include
Lake Tohopekaliga, East Lake Tohopekaliga, Lake Otto, Lake Hart,
Alligator Lake, etc. On a smaller scale it is marked by a line
passing along the southeastern edges of lakes Conlin, Cat, Brick,
Gentry, Cypress, and Pierce. On the assembled photo index sheets
one can see a narrow lineal swamp which extends some 16 miles
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 49
along this essentially straight line. For some few miles northeast
of Lake Conlin along this line any subsequent effects which this
structure may have enforced upon the surface before the last
submergence have been effectively masked by a northern extension
of the zone of progradational bars which form the divide of the
St. Johns and Kissimmee rivers. Farther to the northeast, however,
the trace of the same structure seems able to express itself through
obscure influences on consequent features. Apparently, it controlled
erosional features in the presubmergence topography which in
turn exercised an influence upon depositional and erosional
phenomena accompanying submergence.
Thus although it is impossible to think of Taylor Creek (a minor
tributary of the St. Johns River) as a subsequent stream which
insinuated itself into its present position by headward erosion, it
nonetheless follows a course which seems to express the fault trace.
Other obscure features in the valleys of the St. Johns and Indian
rivers also suggest the same trend, although one is loathe to
accredit the trace of a buried fault with control of such elusive
topographic features as those appearing in alluvial plains or
intracoastal lagoons. However, a projection of this trace intersects
the coastline at False Cape, a matter of considerable significance.
False Cape (fig. 11; pl. 1) is a minor coastal prominence which
appears in the northern part of Cape Canaveral. It would seem
plausible that it has been located by some structurally controlled
erosional feature of the fault trace, which upon submergence acted
as a sediment trap for the sands of the Atlantic beaches that are
known to drift southward.
The False Cape and Cape Canaveral quadrangles suggest that
the present Cape Canaveral is the result of a southward growth
from an original cape located at the site of the present False Cape.
The evidence for this lies in multiple sand ridges, which intersect
the present beach at abrupt angles and extend inland in a
southwesterly direction. These represent successive positions
of the beach built by the clockwise eddy immediately southwest of
Cape Canaveral as the cape built southward under the influence
of the southward moving current. These sand ridges may be seen
on the photo index sheets of Brevard County (shown here as fig.
11). It will be noted that they all terminate landward by curving
gradually southward to merge with the eastern shore of the lagoon
known as Banana River. None of them, however, are truncated
by the shore of the lagoon. Thus it would seem that the shore of
the lagoon is the original beach, or offshore bar which extended
southward from False Cape before Cape Canaveral had begun to
50 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Figure 11
Aerial photographs of eastern Brevard County showing beach ridges, False
Cape, and Cape Canaveral.
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 51
migrate southward. In this connection, it is significant that the
shore of the lagoon intersects the present beach exactly at False
Cape.
Structural or lithologic control of False Cape is strongly
suggested by its geographic stability or multiple recurrence at the
same place in the coastline. A line drawn landward from the
present False Cape shows a succession of relict False Capes, all
essentially coaxial with the present one. The most salient of these
is marked by the western, or landward, shores of the two lagoons,
Banana River and Mosquito Lagoon, which intersect the present
coastline at False Cape, thereby separating Mosquito Lagoon from
Banana River. It was a much more abrupt coastal prominence than
the present False Cape and extended just as far seaward.
Westward, or landward, from both Mosquito Lagoon and
Banana River are multiple beach ridges that are parallel with their
present western shores and apparently represent successive stages
in the growth of False Cape. In reference to the hypothesis that
False Cape is structurally controlled, it is probably significant that
its growth has been seaward rather than longshore and that it has
become less acute as progradation extended it seaward where the
controlling bedrock feature had less and less effect upon shoreline
processes as it was encountered in deeper and deeper water.
The longshore growth of Cape Canaveral suggests that pro-
gradation of False Cape has progressed as far seaward as the
engendering structural feature will permit at present sea level.
Apparently, the rock outcrops are too deep off the present False
Cape to have any further action as a trap for sediment moving
southward along the coast.
From the topographic maps it appears that sea level change
has had little, if any, influence on the coastal evolution described
here, for the beach ridges of all the successive relict shorelines are
at about the same elevation, centering close to 10 feet.
Some evidence that capes have been repetitively present at
successive sea levels along the Cape Canaveral to Indian Rocks
axis may be had from peculiarities of beach ridges in Orange and
Osceola counties. As described elsewhere in this report under
the heading "Relict Beach Ridges as Index to Sea Level Change
and Subsidence," these relict beach ridges occur in a long triangular
zone which narrows to a point at the south and reaches its
maximum width in the area west of Cape Canaveral. This suggests
that an ancestral Cape Canaveral was built at the level of these
beach ridges.
The relict beach ridges of the western half of this triangular
52 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
zone all have crest levels at a fairly uniform elevation of 75 to 85
feet. This suggests that a cape was built by progradation at that
level during a period of stable sea level.
The beach ridges of the eastern half of the zone are successively
lower to the east but still preserve the northeasterly orientation
which suggests that they were formed immediately south of a
series of former capes that were built at successively lower levels
by the successive shorelines of a falling sea level retreating across
a surface that sloped gently seaward to the east.
These relict capes are no longer preserved, apparently having
been destroyed in the development of the St. Johns River valley.
Another suggestion of a relict cape along the cross-peninsular
divide is seen in the convexity of the Pamlico scarp as it appears in
the western valley wall of the St. Johns River opposite the Cape
Canaveral area. It extends 10 to 20 miles farther seaward opposite
the present cape than it does at localities 30 to 40 miles up or down
the coast.
Offshore Sedimentation in the Gulf of Mexico: In the Gulf of
Mexico off the west coast of the Florida Peninsula, the sediments
off the cape at Indian Rocks are different from those to the north
or south in that they are composed of coarser sand. This
information is derived from a map presented by Gould and Stewart
(1955). It is reproduced as figure 12 of this report. From this
map it will be noted that within 20 miles of the present coast the
coarse sand is arranged in elongate arcuate zones arranged roughly
concentric with the present shoreline, and concentrated off the
present capes, most prominently off the cape at Indian Rocks but
also off those at Venice and Sanibel Island.
Capes tend to be points of convergence for longshore currents
flowing in opposite directions. The two opposed longshore currents
combine to form a single current flowing seaward from the apex
of the cape. This suggests that capes have a mechanism which
allows them to reproduce themselves when sea levels are lowered.
The coarse sands, which apparently are deposited as lag gravels
by seaward setting currents, offer more resistance to beach erosion
than do the finer sediments which form the bottom elsewhere along
the coast. Therefore on emergence, they form more stable beaches.
Although this argument suggests that many capes have a
reproductive mechanism in the form of these lag gravels, it may
be seen from figure 12 that the largest area of coarse sand is a coast-
parallel zone located some 50 to 75 miles offshore, but with a large
triangular protrusion extending landward with its apex located
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 53
Figure 12
Map showing bottom sediments off the west coast of the Florida Peninsula.
immediately offshore from the cape at Indian Rocks, and its central
axis located along an extension of the line between Cape Canaveral
and Indian Rocks. This suggests that a more powerful seaward
setting current is located off the cape at Indian Rocks than off the
other capes to the south. An assumption that such a current has
persisted in the same place through fluctuations of sea level might
help to explain the subaerial features along the Cape Canaveral-
Indian Rocks axis which the writer has described above, for it
would imply that a succession of capes had formed along this line
at successive shorelines as sea level changed.
THE QUESTION OF WESTWARD TILT IN THE
FLORIDA PENINSULA
There has long been a considerable opinion among geologists
that the peninsula has been tilted downward to the west, or Gulf
of Mexico side, in late geologic time. The basis of this opinion is as
follows:
1. Observations by Leverett (1931) who thought the Pensacola
(Pamlico) shoreline was higher on the Atlantic side of the peninsula
than on the Gulf of Mexico side.
54 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
2. The presence of large estuaries on the west coast, i.e., Tampa Bay,
Charlotte Harbor and possibly Florida Bay.
3. Drowned karst, or sinkholes, in the shallow marine water along the
northern part of the west peninsular coast.
4. The presence of a great re-entrant in the west coast of the peninsula
between Apalachicola and Anclote Key.
5. The fact that the surface of the Florida plateau (the large area which
rises from profound oceanic depths to form peninsular Florida and the
large area of shallow sea bottom to the west of it) is subaerially
exposed on its eastern edge as the Florida Peninsula, but becomes
progressively more deeply submergent to the west.
It is the writer's opinion that there has been no late tilting of
the peninsula and that the criteria that suggest it are in some cases
misleading, in others erroneous. They are discussed below in the
order listed above.
Evidence for Tilted Terraces: Leverett identified the shorelines
of the Pensacola terrace at elevations of 40 to 45 feet on the east
coast and about 30 feet on the west coast, in the vicinity of Tampa
Bay. The writer finds no difficulty with his observations on the
west coast, but on the east coast he studiously avoided recognition
of a 30-foot scarp base as Pamlico on the basis that it was a fluvial
feature of the St. Johns River rather than a reflection of a former
sea level.
As the east coast correlative of the 30-foot scarp base on the
west coast, he selected instead a more obscure scarp base at ar
elevation of about 40 feet, possibly a correlative of the Talbot scarp.
Regardless of what this 40-foot scarp base may represent, it is
difficult to regard the 30-foot one as a fluvial feature independent
of any sea level. It is far more persistent than the 40-foot feature.
It can be found quite commonly for a distance of some 200 miles
along the valley wall of the St. Johns River, and it maintains a
uniform elevation very close to 30 feet throughout this distance.
It would be most difficult to conceive of a fluvial terrace 200 miles
long and uniform in elevation, unless it were produced by estuarine
conditions and controlled by a sea level.
Leverett did exemplary work in tracing the Pamlico terrace at
a time when few maps or aerial photographs were available and it
is not the writer's intention to detract from the value of his work.
However, a glance at the numerous large scale topographic maps
now extant reveals geomorphic information which was quite
unavailable to him. The classic Interlachen sheet was then available.
It shows a prominent 40-foot scarp base although elsewhere on
the many maps now at hand, the 30-foot feature is much more
widely prominent.
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 55
Again Leverett seems to have been given misleading information
concerning elevations on a highway grade in a critical place. Thus
he says (1931, p. 26), "the profile of a highway running west from
Melbourne into Osceola County shows the change from the flat to
more steeply inclined surface near Deer Park to be at 43 feet
above present sea level." The 7.5 minute Deer Park sheet (fig. 13)
Figure 13
Northeastern part of Deer Park sheet showing Pamlico scarp with crest at
elevations approximating 45 to 50 feet.
56 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
now available shows a highway climbing an abrupt scarp in the
vicinity of the town of Deer Park, but the crest, rather than the
base, of the scarp is in the vicinity of the 45 and 50-foot contours.
Its base is at the 30-foot contour, where the land flattens out on
the St. Johns River fluvial plain. Thus Leverett seems to have
been misled into correlating the 45 to 50-foot crest of a scarp in
Osceola County with the 40-foot base of a scarp near Interlachen.
Leverett's only specific reference to an inland locality where
the Pamlico shoreline crosses the peninsula is at La Belle where
he says the altitude is about 35 feet. There still are no topographic
maps for this locality, but an elevation of 35 feet is close enough to
the usual 30-foot figure to offer no appreciable discrepancy.
Neither Cooke nor MacNeil found any difference between the
elevations of the Pamlico shoreline on the east and west coasts, and
the writer can see nothing in Leverett's observations which might
support the idea of regional tilt, even though one must recall that
crests of depositional scarps may correlate roughly with bases of
contemporaneous erosional scarps.
Cooke stated (1939, p. 40):
. as long ago as 1913 . Matson described . the Pensacola
terrace . .he recognized two levels, which correspond to the Talbot
and the Pamlico. A later unintentional correlation (by Leverett) of the
shoreline of the upper Pensacola level (Talbot) on the east coast with
the shoreline of the lower level (Pamlico) in West Florida resulted in
the interpretation that there had been a slight downwarp on the
Pensacola toward the west."
Evidence of Tilting from West Coast Estuaries: The writer
also finds it difficult to regard the west coast estuaries as evidence
of regional tilting. There are several factors involved in this
opinion. In the first place estuaries are not limited to the west coast,
but are found on the east coast as well. Perhaps those on the west
coast have been more conspicuous because they indent the shoreline
more abruptly and are generally wider and more baylike than those
of the east coast, which are narrower and more lineal in form. Thus
the St. Johns River bears little resemblance to Tampa Bay or
Charlotte Harbor, but it is nonetheless an estuary in its lower
reaches.
Broad bay-like estuaries have less chance of forming on the
east coast because of the voluminous southward drift of sand along
the Atlantic beaches. This has built a broad zone of closely
spaced progradational beach ridges which effectively prevent the
preservation of wide shallow bays. Thus the present coastal area
on the Atlantic side of the peninsula has evolved from the deposition
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 57
of a succession of sand bars and beach ridges, which have been
built progressively seaward as sand drifted down the coast from
source areas to the north. Such sand ridges can be seen very
clearly on aerial photographs (fig. 11) and topographic maps of
the False Cape and Cape Canaveral area in Brevard County. The
seaward growth of such multiple ridges would dominate the pattern
of the lower courses of streams. The streams would have to
elongate themselves, flowing between the beach ridges as these were
built across their mouths. Thus in areas of heavy beach and bar
building most coastal drainage would be dominated by long coast-
parallel streams. On the Florida east coast the St. Johns River
exemplifies this fact with its unusual extent of 200 miles parallel
with the coast.
As sea level fluctuated, bars and beach ridges would be built
in different localities as the shoreline migrated in and out. In the
situation now presented by the Florida east coast, it would seem
that multiple or progradational offshore bars, built during Pamlico
or Talbot time, determine the course of the St. Johns River, for
these bars are the highest land between the St. Johns River and
the present coast. Following the withdrawal of the Pamlico sea,
part of the valley was trenched by the river to depths as much as
110 feet below present sea level. This is shown by test borings made
for the former Florida Ship Canal Project (Stringfield, V. T.,
personal communication to Gunter, Herman). With return of a
higher sea level the valley was flooded, probably more extensively
than at present during the time known as the Thermal Maximum,
a few thousand years ago when sea level seems to have been
slightly higher than at present. However, present sea level is high
enough to maintain estuarine conditions in the St. Johns River
for many miles upstream.
Although the Indian River is clearly a lagoon behind an offshore
bar rather than an estuary, the St. Lucie River, of Martin and St.
Lucie counties, seems to be an estuary even though the configuration
of its shoreline suggests control by beach ridges.
The longevity of the Atlantic's habit of building progradational
beach ridges along the Florida east coast is shown by the ubiquity
of such ridges in the eastern half of the peninsula. In stair-like
progression they appear in groups which dominate successive
terrace surfaces. The highest of these can be seen on the aerial
photographs of Polk County in the Lake Wales Ridge area. A
lower group is seen in Orange and Osceola counties, and a still
lower one in the area drained by the Econlockhatchee River. Lowest
of all, the multiple ridges of the present cycle are exceptionally
58 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
well shown in the Cape Canaveral and nearby sheets, and on the
aerial photographs of Brevard County (fig. 11).
Since this habit of building progradational beach ridges has
been characteristic of the Atlantic or east coast for so long, streams
would have had great difficulty developing or preserving broad
open valleys at right angles to the coast. Instead it would be their
habit to debouch into narrow arterial avenues which were originally
conceived as coast-parallel lagoons, such as the present Indian
River.
The estuaries of the west coast are quite as readily explained as
the result of a rising sea level as by a regional westward tilt. To
a considerable degree they can be explained as water bodies which
have become surrounded by constructional marine features.
Although there is little evidence of progradational beach ridges on
the west coast of the peninsula, the estuaries are located opposite
the openings or inlets in offshore bars of the present coast. From
the map (pl. 1) it will be seen that the offshore bars are integrate
with the mainland at points midway between estuary mouths. The
most northerly offshore bar of the peninsular west coast is Anclote
Key, which lies off the estuary of the Anclote River. St. Joseph
Sound, between the offshore bar and the mainland shore, narrows
progressively in a southward direction until the bar is in essential
contact with the mainland at Indian Rocks, midway between
Anclote River and the mouth of Tampa Bay. Similarly, Boca Ciega
Bay widens southward from Indian Rocks to Mullet Key at the
mouth of Tampa Bay. A very similar relation is seen between
offshore bar and mainland between Tampa Bay and Charlotte
Harbor. Here Sarasota Bay narrows southward to its head near
Venice, where it is integrate with the mainland, and Gasparilla
Sound widens southward toward the mouth of Charlotte Harbor.
South of Charlotte Harbor and the Caloosahatchee estuary, Estero
Bay narrows southward to a point north of Naples where the
offshore bar which encloses it becomes attached to the mainland.
This relationship might suggest that the present bays are
largely areas of former shallow sea bottom, which have been
enclosed by ocean-built shoreline features as the sea retreated. That
this habit of bar building has been repetitive is suggested by
features farther inland which also seem to have separated offshore
bars from the mainland. Thus on the Oldsmar and Elfers sheets
it can be seen that Lake Butler (Lake Tarpon) and old Tampa Bay
occupy a coast-parallel swale which intersects the present coast
near Elfers, due east of Anclote Key. The continuity of this
largely water-filled valley is very clearly seen from the air and even
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 59
to the casual observer it is obvious that it was once a continuous
seaway connecting Tampa Bay with the Gulf of Mexico west of
Elfers. The Port Tampa Peninsula separates this broad swale
from a similar one farther east, which holds Hillsborough Bay.
Similarly, between Tampa Bay and Charlotte Harbor the lower
Braden River, in Manatee County, and the lower Myakka River, in
Sarasota and Charlotte counties, follow a long coast-parallel valley
which terminates at the south in Charlotte Harbor and the sound
that lies between Pine Island and the mainland. This long trough
seems to be the same one that is occupied by old Tampa Bay and
Lake Butler and it will be noted that it terminates at both north
and south ends by running into the open sea at places where the
shoreline has not been built seaward. In other words, the zone of
present and past offshore bars has the same extent, one end being
at Anclote Key-the northernmost of the present offshore bars,
the other at Sanibel Island where the present coast turns abruptly
eastward.
Further support for the idea that the great estuaries of the
west coast are largely areas of former shallow sea bottom,
surrounded by constructional shoreline features, can be had from
the fact that estuaries are either absent or small in those parts
of the west coast where beaches and bars do not readily form. Thus
in the great coastal re-entrant between Apalachee Bay at the north
and Anclote Key at the south there are no estuaries of note. The
two largest streams, the Suwannee and Withlacoochee rivers, have
no estuaries. Two streams of secondary size, the Steinhatchee and
Waccasassa, debouch into bays (Deadmans and Waccasassa bays),
which indent the coast very little and are broadly and obtusely
open to the sea. In the vicinity of Homosassa and Crystal rivers
several small streams are very narrowly estuarine for short
distances. None of these features resemble either in shape or size
the large land-locked embayments of the sand dominated section
of the west coast between Anclote Key and Naples.
The absence of an estuary on the Withlacoochee River is
probably the result of a recent change of course in the river,
possibly a similar explanation for the lack of an estuary on the
Suwannee River may hold, but when one considers that many of
these rivers, like the Waccasassa occupy broad shallow valleys, it
is difficult to explain their lack of deeply re-entrant estuaries if
there has been either late sea level rise or westward tilting of the
regional land surface. The writer has difficulty avoiding the
conclusion that the divergent features of these two sections of
the Gulf Coast are the result of two different regimes of coastal
60 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
environment. Perhaps the essentially sand free coast manages to
build itself up in the vicinity of these river mouths because of the
beneficial effects of phosphates in the river water on the growth
of mangrove and other littoral vegetation. Some credence may be
lent to this idea by the fact that most strandline vegetation suffers
a phosphate deficiency because of the low concentration of
phosphates in most sea water, and these rivers drain the largest
accumulation of phosphate deposits in the United States.
On the other hand, in the sand dominated coasts, perhaps the
mangrove may be overwhelmed by the sand which builds bars
parallel with the shore, from the most salient points on the coast
toward the more re-entrant places. The salients most plausibly
would be stream divides and the re-entrants, stream valleys. The
shore would build seaward in a series of offshore bars, which were
most widely separated opposite the stream valleys, forming such
embayments as Tampa Bay and Charlotte Harbor.
Such offshore bars would not prograde in a successive
development of closely spaced ridges like those of the east coast,
which are more voluminously supplied with sand. Only a single
line of bars seems to have been built here at the present sea level,
while on the east coast multiple beach ridges at the present level
are common (fig. 11). There is considerable suggestion that the
bars built by higher sea levels farther inland in the Anclote Key-
Sanibel Island section of the coast, were also rather widely spaced,
leaving room for the present embayments between them.
It is obvious that the features just described are not wholly of
themselves capable of producing such an embayment as Tampa
Bay. Miocene sediments extend well above present sea level in
the areas covered by the old sand bars which now separate old
Tampa Bay from St. Joseph Sound and Boca Ciega Bay. Apparently
there has been extensive subaerial reduction of these large
embayments during glacial stands of low sea level, just as there
has been in the lower St. Johns River on the east coast. This no
more implies seaward tilt here than in the case of the St. Johns
River.
Why Tampa Bay and Charlotte Harbor are localized where they
are is not quite clear. Hillsborough Bay and Tampa Bay proper
may have been formed as the valley of the Hillsborough River
which may once have been the outlet for most of the present
Withlacoochee River drainage area. This is suggested by the
alignment of the two parts of the bay with the present Hillsborough
River, and with the upper Withlacoochee River. However, it is
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 61
peculiar that the estuarine condition ends abruptly at the head of
Hillsborough Bay in the vicinity of Tampa with no graduation or
preliminary narrowing. Again, old Tampa Bay and the obviously
congenital Lake Butler to the north have no apparent relation to
any large stream. Moreover, old Tampa Bay is fairly equidimen-
sional and rather bottle-necked, and Lake Butler drains through
an underground solution avenue (Heath, 1954). Possibly these
observations can be explained by the fact that both Tampa Bay
and Charlotte Harbor areas are underlain by surficial exposures of
the Caloosahatchee marl. These are the only two places where this
formation is exposed near the coast. Elsewhere, in the sand
dominated section of the west coast (Anclote Key to Sanibel
Island), less soluble and less permeable rocks are at the surface.
This would suggest that these re-entrants of the coastline are
largely the result of solution within the Caloosahatchee which
took place during times of low glacial sea levels. Perhaps this
idea is facilitated by the fact that Tampa Bay and Charlotte Harbor
are in places where the piezometric surface is well above sea level
at the coastline. Apparently, this is made possible by the presence
of the rather impervious Hawthorn formation, which underlies
the soluble and pervious Caloosahatchee. This combination of a
high piezometric surface, an impermeable substratum to exclude
artesian water, and a permeable and soluble surface layer could
promote broad solution depressions by lateral movement of ground
water since there would be no opportunity for surface water to
enter the artesian system and escape by downward circulation.
However, this idea is offered with reservation.
The effect of mangrove in preventing the formation of coastal
re-entrants is shown by the Ten Thousand Islands, and possibly
this may be the reason that Cape Sable has built itself seaward
opposite the point of principal fresh water discharge from the
Everglades. Such growths would become very effective sediment
traps to catch any small amount of sand which might enter the
area.
Florida Bay, the largest estuary-like re-entrant in the peninsular
coastline, is enclosed by constructional marine shoreline features,
the Florida Keys. Although there are factors involved in the
making of Tampa Bay and Charlotte Harbor which are absent
here, and vice versa, this may possibly be used as a case in point
to suggest that embayments can result from progradational, rather
than submergent, influences. Nonetheless, although the writer has
felt it desirable to bring out the apparent influence of the shore-
built features in the development of Tampa Bay and Charlotte
62 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Harbor, it is his belief that these embayments are in considerable
measure the result of eustatic sea level rise.
Drowned Karst: The presence of drowned sinkholes along the
northern part of the Gulf coast, like the estuaries, is evidence only
of submergence. They could just as easily have been submerged
by eustatic sea level rise as by westward tilting of the peninsula.
Their absence on the east coast is easily explained by the voluminous
deposition of sand which would quickly fill and conceal any
submerged solution depression.
Coastal Re-entrant between Apalachicola and Anclote Key: This
great coastal re-entrant (pl. 1) is coextensive with the section of
the Gulf Coast in which the Eocene and Miocene limestones are
exposed at the surface. It is distinguished from the great coastal
salient, or sand-dominated section of the coast (Anclote Key to
Naples), by the fact that the region behind this more southerly
section is surfaced generally by younger formations which are
largely insoluble and frequently of rather low permeability. It
would seem to the writer that this alone would explain the great
re-entrant for its soluble limestones should be more readily reduced
than the insoluble formations of the great salient. Cooke, however,
thought the re-entrant was evidence of westward tilting. He states
(1945, p. 5) :
"The Floridian Plateau north of St. Petersburg has been tilted downward
toward the west. This tilting accounts for the broad embayment of the
west coast of Florida between Clearwater and Apalachicola. It has
caused the submergence of the western part of the Ocala uplift, in which
the bands of outcrop of the Ocala, Suwannee, and Tampa limestones are
truncated by the coast line. It also accounts for the absence along the
embayed area of those marine Pliocene formations that cover nearly all
of southern Florida and extend all along the east coast. To some extent,
however, these effects may be the result of the greater degradation of
the part of the Floridian Plateau covered by soluble limestone. It may
be significant that the embayed area is bordered throughout by soluble
limestones. Moreover, it is quite likely that the submerged Miocene
formations on the Plateau are composed of more soluble materials than
those formations that crop out on the land, which contain much sand,
for the submerged parts are farther away from sources of plastic
sediment."
The writer admits that an early tilting of the Florida plateau
in general seems plausible, but it is difficult to see it as a reason
for the great coastal re-entrant. Many essential differences between
the re-entrant and salient parts of the coast suggest that the
re-entrant is the result of denudation and the salient the result
of construction and resistance to denudation.
Thus the two largest rivers of the west coast, the Suwannee
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 63
and the Withlacoochee, debouch into the re-entrant. Furthermore,
as discussed elsewhere in this report, the Withlacoochee seems to
have been captured by the re-entrant coast from a former
debouchure in the salient coast.
Again, the land surface is notably higher along the salient
coast than it is along the re-entrant coast, suggesting greater re-
sistance to denudation.
The great springs in the peninsula are in considerable measure
concentrated in the region of exposed limestone along the re-entrant
coast, and the principal area of recharge to the great limestone
aquifer is opposite it. Thus if this region has at once the greatest
rate of recharge in one area and nearby a high rate of discharge, as
manifest by the many great springs and the rivers of large
discharge, it would seem most plausible that it should be an area
which is being wasted rapidly by solution. Still further evidence
of the higher rate of discharge of ground water through the rocks
of this area may be had from the fact that it has flushed the salt
water out of the aquifer save for a narrow local strip along part of
the coastline. Along the eastern and southern parts of the peninsula
much of the salt water still remains in the aquifer because the
impermeable caprocks have prevented its escape. The fact that
there are no estuaries on the big rivers which debouch into the
great coastal re-entrant, may suggest that there has been no late
tilting here. However, this idea is subject to the limitations
imposed by whatever truth there may be in the writer's speculations
(above in this report) about the influence of mangrove in building
the mouths of these streams seaward. Also, Cooke explained the
absence of estuaries here by postulating that the present lower
courses of the rivers went underground during times of low sea
level and therefore have cut no valleys.
Submergence of the West Side of the Florida Plateau: The
fact that the Florida plateau is above sea level on its eastern side,
and increasingly deeper below sea level to the west, has been a
strong argument for regional westward tilt. With this idea the
writer has no quarrel, but if such tilting did take place, it was at
a time so long ago (probably pre-Pleistocene) that it has left no
presently recognizable effect on the topography of the peninsula.
Evidence from the Everglades: The most positive evidence
against late tilting of the peninsula can be had from certain aspects
of the drainage of the Everglades and surrounding areas of the
extreme southern peninsula. The map (fig. 14) showing contours
on the rock floor of the Everglades, made by the Soil Conservation
64 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
31 32 33 34 35 3M 3T 38 SO 40 4A
N O ST. LU@
I, .; . .
c LA iS
m A f I
EXPLANATION
-I- COnTOuIS On TOP OP AOC1
ALL CONTOURS ARE 44A1 TO OEAC@I CN
US e R A AIRI.
SUOO*CT A FEET 1 a 0Im ICtUS RiVIE
INCR TO CONVENT TO S. L.
SCALI IN MILES
A O J
fOprto FROm MAP @r
u s O,,r Or Af'iCUTtT
so,. cast varToe sIRwICi
CONTOURS ON THE ROCK FLOOR OF THE EVERGLADES
Figure 14
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 65
Service of the U. S. Department of Agriculture (also presented
as plate 12 of Florida Geological Survey Bulletin 27) reveals two
channel outlets from the Everglades. The larger and more
prominent of these extends some 30 miles in a southwesterly
direction toward Cape Sable along the principal axis of drainage
drift. The other is New River, which cuts across the Atlantic
Coastal Ridge in a general direction, a little south of east, emerging
on the coast at Fort Lauderdale. Both these channels are unusually
acute in cross section by comparison with the slopes seen elsewhere
in the general region of the Everglades, and both are obviously
erosional features produced by the water which has discharged
through them. They have bottlenecks where they narrow to the
extent that the contours are so close together they cannot be
distinguished individually. The lowest place in each of these
narrows is the same height. The three-foot contour, the lowest one
shown on the map, runs through both narrows and widens out to
depict a broad flat floor between them. In other words, the
minimum elevation of the bed rock surface in the Everglades region
is three feet, and the region may be crossed from the Atlantic Ocean
to the Gulf of Mexico without exceeding this elevation, by following
these two channels and the broad lowland connecting them.
It is difficult to know how long this transpeninsular valley has
been in existence in its present state of reduction, but certainly
there has been no tilting of this part of peninsular Florida since
its present floor was established. Although this criterion of stability
is limited in both the area and the period of time to which it is
applicable, it is very sensitive within these limits. Most
particularly, it suggests that Florida Bay is not the result of
westward tilt.
FLORIDA LAKES
The innumerable lakes of the Florida karst country are one of
the outstanding peculiarities of the State. This lake region has no.
counterpart in North America, for although a few small sinkhole
lakes are found in other regions of karst topography, nowhere is
there such an extensive zone of closely spaced solution-basin lakes.
The literature on these lakes is small. In 1890 Shaler ascribed
the peculiarities of peninsular topography to original irregularities
in the surface of sand deposited by the Gulf Stream at a time of
high sea level. According to this idea the lakes merely occupy
basins in this irregular surface.
66 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
Shallow Lakes: Sellards (1910) was the first significant student
of Florida lakes. Writing of the large lakes north of Tallahassee
(Lake lamonia, Lake Lafayette, Lake Jackson, and Lake
Miccosukee) he ascribed their origin to dismemberment of a former
stream system through the agency of capture of subterranean
drainage. He noted that each one of these lakes had a sinkhole
somewhere in its periphery where the shore lay under a relatively
steep bluff. On this observation he based a hypothesis which
assumed that the lake basins had been excavated by a sequential
development of similar sinks, the earlier ones being filled with
sediment while the newer ones developed along the shoreline.
Lakes of this "Sellards type" are found also in the upper
peninsula in Marion and Alachua counties. There the former
Alachua Lake or Payne Prairie shares all the peculiarities of those
described by Sellards, and nearby Levy and Newnans lakes also
appear similar in that their basins have high rims and no surface
outlets. Farther south, however, large lakes nearly all have surface
outlets and, although some of the basins they occupy have high rims,
there are no sharply re-entrant sinks along them. Others like
Lake Kissimmee lie wholly in low surroundings.
The writer believes these more southerly lakes represent an
earlier stage in the process of development than do the more
northerly ones, the latter being now in the process of slow
destruction. In each of the large lakes described by Sellards, there
seems to be only one sink through which water may drain to
subsurface discharge. This would seem to be evidence against the
idea that such lakes have been formed by multiple sinks. It would
be a remarkable coincidence if a basin developed by multiple sinks
could manage to have each successive one plugged just at the time
a new one appeared. In multiple sink basins there should be a
number of plugged sinks and a number of open ones. Conversely,
if the sinks are the cause of the lake's demise rather than its
development, there should characteristically be but one sink (or
at the most a very few) in each lake for the first sink formed
should be sufficient to drain the lake whenever the water table
dropped below the level of its bottom. Thus in the vicinity of the
famous disappearing Alachua Lake near Gainesville there are
several prairies (Sanchez, Kanapaha, Hogtown, etc.) all of which
drain through single sinks and give every evidence of being extinct
lakes drained by a lowered water table, or a lowered piezometric
surface.
The writer is inclined to disagree with Sellards' suggestion that
the lakes have been made in the process of dismembering the former
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 67
stream systems. Rather, the writer thinks these-now decadent,
disappearing-lakes had surface inlets and outlets during their
more stable former existence, just as the present large stable lakes
along the St. Johns, Kissimmee and Oklawaha rivers do. Sellards
noted that all four of the Leon County lakes (Lake Jackson, Lake
Miccosukee, Lake lamonia and Lake Lafayette) occasionally have
surface drainage during periods of heavy rainfall. This suggests
that they once had continuous surface drainage when the
piezometric surface was higher and the water table more
permanent. If the basins occupied by these lakes were formed by
undermining and collapse of former stream systems it would be
remarkably coincidental that all four of them are still able to
drain via the old stream valleys at times of high water.
In other words the writer feels that the lakes antedated the
dismemberment of the stream systems, and are themselves now in
the process of dismemberment just as the streams are, the only
thing that preserves them being a water table-perched or not-
which is sometimes above the level of their bottoms.
Unlike Sellards the writer feels that the dismemberment of
streams took place, not because of the new development of solution
avenues, but through the utilization of solution avenues which were
already extant when the piezometric surface and water table fell,
although new breakthroughs from the surface may have made the
sinks. The writer doesn't think these lakes were formed during
the present period of perched water tables, rather that they are
precariously preserved by the perched water tables.
Some aid to this hypothesis may be had from the support which
the water that fills a subterranean opening gives to the roof of the
opening. When the water table falls such openings are drained
and become air filled. The air lends little support to the roof of the
opening and collapse is more likely to occur. To the best of the
writer's knowledge, most places where such collapse has been ob-
served in the act of occurrence have been in areas where air-filled
caverns underlie the surface.
The presence of a sink through which a large, shallow, flat
bottom lake obtains its drainage should be a detriment rather than
a help in stabilizing either the level of the water in the lake or the
level of its bottom. For there would be no lake if the sink connected
with an underground avenue of discharge sufficiently unrestricted
and of adequate gradient to discharge the total amount of water
which would feed into the lake if it could be drawn down below
the level of the water table in the surrounding terrain. In such a
situation a dry sink would occur instead of a lake. The presence of
68 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
water in a lake is evidence that any sinks in its bottom are, for
the time being at least, inadequate to drain it. When plugged sinks
in the bottom of perched lakes (such as Alachua sink in the former
Alachua Lake) become unplugged, the lakes are peremptorily
drained. Actually, in this type of lake, it seems more plausible that
the sink is the result of the presence of the lake rather than the
lake being the result of the sink. That is, the presence of a broad
body of acid water standing over fractured limestone would
facilitate downward movement and solution. But if downward
movement became too voluminous, the lake would drain and a
swampy or even dry basin would replace it. Many of Florida's
swamps and prairies may have originated in this manner during
times of low-water table.
Again, large shallow lakes which now drain through sinks are
to the best of the writer's knowledge all of the disappearing sort.
They are found in areas where the water table and piezometric
surface seem to have fallen, and although now precariously
preserved by perched water tables, their basins were probably
excavated under more stable conditions of water table. They might
be classified as decadent lakes, and as Sellards observed, several
of them occur in the valleys of former streams that have been
dismembered by underground capture. The sinks through which
they now drain may or may not antedate the dismemberment of
the streams but they now are more a mechanism of the lake's
destruction than of its development.
If a lake is at once large in area, shallow in depth, and flat of
bottom, there is a strong suggestion that the same factor which
determines the level of its surface also determines the level of the
flat bottom that so closely parallels that surface. This factor
seems to be the water table as Sellards suggested, but it does not
seem to operate through the mechanism of sinks as he thought.
He believed that the lake basins were excavated by a succession
of sinks, only the most newly formed of which were active at any
given time, the older ones having been filled with sediment to the
level of the flat lake bottom. His strongest argument for this
hypothesis was the marginal location of the sinks in several of the
large "disappearing lakes." But the writer suspects that the
presence of these sinks may well be the reason the lakes are of the
disappearing sort, and their marginal location may result from
the fact that they did not share the muck or clay seal of the lake
bottom.
The writer feels that the water table determines the level and
flatness of the lake bottom because it is the level at which a
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 69
maximum lateral discharge of ground water takes place, especially
in terrain where permeable sands overlie soluble limestone that
is sufficiently impermeable to hold the water table up in the sands
much of the time. In an originally flat terrain such a dominantly
lateral movement of ground water at the water table might exercise
a close vertical control on the depth to which solution could readily
go, and could hardly fail to produce a flat surface slightly below the
water table.
Also once the lake was formed the development of a layer of
organic muck on its bottom might well seal its waters off from the
underlying limestone and prevent further deepening. The idea that
such mucks are largely impermeable is widely current among
Florida geologists.
On the other hand, there is no reason why multiple sinks should
produce either flat surfaces or surfaces which closely parallel the
water table, for the sinks are the result of downward rather than
horizontally moving water. In special instances the presence of an
insoluble and impermeable stratum might cause sinks to bottom
at the same horizon. But this could not cause them to bottom
uniformly a few feet below the water table throughout the whole of
the Florida lake country, for the structural situation underlying
Florida's many large lakes is highly diverse.
Also it might be argued that enough sediment could be carried
into a lake to fill sinkholes and choke them into inactivity while
new ones would form from undermining elsewhere, probably at
the edge of the lake where it was extending itself by their
successive development. But many of the broad shallow lakes of
Florida have no inlets and most of those which do have inlets are
fed by sluggish streams which appear to carry very little bed load.
Rarely do lake head deltas form at the mouths of the inlet streams,
although there are small ones at the heads of Lake Tohopekaliga
and Lake Arbuckle.
What one might expect from sinkhole development is manifest
in the smaller lakes which are so frequently deeper than the large
ones. They are differential in depth, and although their surfaces
may reflect the water table, their bottoms do not.
The fact that most known springs have relatively small head
pools leads to the inference that vertical movement of ground water
does not readily produce broad shallow basins. Of course, there
may be more recharge than discharge pipes, and in many instances
it seems evident that multiple recharge pipes, with funnel-shaped
cross sections have widened their upper parts until they have
coalesced to make lakes of considerable area. Crooked Lake,
70 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
between Babson Park and Frostproof in Polk County, and Lake
Josephine, south of Sebring in Highlands County, are excellent
examples of this (see fig. 9).
Nonetheless, most of the large lakes do not seem to have been
formed by such a coalescence of recharge pipes for their bottoms
are almost reliefless, their shorelines are smoothly curved with
neither sharp salients or re-entrants, they are uniformly shallow
with bottoms little below the water table of surrounding areas,
and for the most part their surfaces lie well below the piezometric
surface which would assure that if they have any connection with
artesian circulation, it would have to be as an avenue of discharge
rather than recharge.
However, there are also difficulties with the hypothesis of lake
basin excavation through solution by horizontal movement of
ground water. Chief among these difficulties, is the removal of
the insoluble material which so characteristically overlies the lime-
stone in the areas around the big shallow lakes. Possibly the lakes
are localized where such insoluble cover was thinner than in the
surrounding area. Vernon (1951) has shown that the Miocene
sediments were deposited on a limestone surface of some
considerable relief, and as discussed below in this report, the large
lakes are found over the high places in this pre-Miocene topography.
However, this would not account for removal of post-Miocene sand
cover. But residual limestone hills are characteristically
honeycombed with air-filled caverns. These would offer ready
admission to artesian circulation after burial by younger sediments,
thus accelerating solution and permitting collapse and inversion
of relief.
Another hypothesis which may possibly explain the absence
of the overburden of sand in certain of the broad shallow lake
basins might be found in assuming that these lakes occupy places
where former shell beds have been leached out of the overburden.
There is plenty of precedence for the existence of shell beds in the
Florida Peninsula, and leaching of such beds may well have
contributed to the formation of some of the depressions occupied
by the present lakes. However, certain rectilinear attributes of
the shorelines of many of the peninsular lakes argue against this
being the principal means of forming lake basins. Throughout the
entire peninsula two dominant trends of structural fractures are
repeatedly manifest by linear trends in the orientation of streams
and elongate lakes and swamps. Many of these lineaments have
been recorded by Vernon (1951). These two linear trends appear
as controlling factors in the orientation of lake shores frequently
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 71
enough to assure that the lakes owe their basins to solution in the
limestone bedrock, rather than in superficial lenses of uncon-
solidated shell beds which are too young to have shared the tectonic
stresses which produced the controlling fractures in the bedrock.
These fractures may be faults which have displaced the bedrock
sufficiently to juxtapose rocks of different resistance to solution, so
that the widening of the lake takes place in the more soluble rock
and is arrested where the less soluble rock is encountered at the
fault trace.
Of course, it is quite possible that the leaching of a lens of shell
material in the superficial formations could account for the absence
of overburden on the bedrock limestone, while differential solution
of the underlying limestone itself accounts for the structurally con-
trolled lake shores. The removal by solution of the overlying shell
material would let the water table down on the underlying limestone
where solution would continue. Vernon has called the writer's
attention to an instance where this has happened in Washington
County in western Florida. There in the "Deadens" shell marl of
the Choctawhatchee stage underlies pervious sand and rests upon
difficultly soluble dolomite of Chipola age.
Further argument for the excavation of lake basins by hori-
zontally moving ground water, can be found in the fact that nearly
all very large lakes have surface outlets, and most of them also
have surface inlets. Examples are Lake Okeechobee, Lake
Kissimmee, Lake George, Lake Harris, Lake Eustis, Lake Griffin,
Lake Istokpoga, Lake Panasoffkee, Lake Monroe, Lake Harney,
Lake Jessup, Lake Arbuckle, Lake Weohyakapka, Lake Dexter,
Lake Crescent, Lake Kerr, Lake Poinsett, Lake Winder, Lake
Washington, Lake Orange, Lake Santa Fe and Lake Tsala Apopka.
Exceptions are Tohopekaliga, East Tohopekaliga, Newnans and
Levy lakes. However, most of these show evidence of once having
had outlet streams. And several of them now drained by canals
may well have had natural drainage through swampy forests with-
out any recognizable channel.
For the most part these inlets and outlets are the biggest
streams of the peninsula, such as the Oklawaha, St. Johns,
Kissimmee, and Withlacoochee rivers. This implies that these
large shallow basins are developed in areas where there is a major
movement of water in the lateral dimension not far from the
surface of the ground. Moreover, the presence of a surface outlet
assures that a lake will retain a reasonably stable water level, for
increased discharge of water into the lake will readily be
compensated by a complementary increase in the discharge of
72 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
water through the outlet. And since the increase in discharge
begets an increase in velocity, the rise in water level of the outlet
stream and lake is not ordinarily excessive. Thus the lake is likely
to enjoy a considerable longevity at a fairly uniform surface level.
Of course, it might be argued that the outlet stream would incise
its channel, lowering both outlet and lake level, but most of the
surface streams which drain the large peninsular lakes are clear
water streams that have very low gradients and do not seem to
show much tendency toward incision.
These several factors-longevity, uniformity of level, and large
volume of laterally moving water-should all be conducive to
widening the lake. Hence it would seem to be more than mere
coincidence that the largest lakes are threaded along the largest
streams.
Conversely to all this, a lake which has no surface outlet, but
drains through a sink instead, will be subject to more extreme
changes of level. For the sink and the avenues of subterranean dis-
charge with which it connects must offer a somewhat restricted
outlet, else the lake would drain entirely. Such a lake will behave
much like a wash basin with a partially obstructed drain, the level
of the water surface will rise when inflow is increased beyond the
capacity of the drain and fall when inflow is decreased to less than
the capacity of the drain or the drain capacity is increased. Thus
the well known disappearing lakes of Florida, such as Lake lamonia
and Lake Alachua, during periods of drought may empty themselves
of water entirely. Even here, however, the lateral movement of
water seems to be the dominant agent in excavating the lake basin,
for nearly all sinkhole lakes, of all but the very smallest size, have
broad gently sloping shoulders of shallow water surrounding the
sinks which drain them. However, these may be in part the result
of inwashed sediment. Many lakes of moderate size seem to have
been formed by coalescence of the shallow waters overlying such
shoulders in two or more adjacent sinks, as in the case of Lake
Josephine and Crooked Lake mentioned above.
This report is concerned with the origin of the basins which
hold the lakes rather than the regimen of the lakes. Their regimen
is a complex matter involving such factors as fluctuation in
precipitation, water table, and discharge of inlet streams, height
of the piezometric surface, permeability of the lake bottom,
evaporation from the lake surface, transpiration from aquatic
vegetation, and loss of water to underground discharge or reception
of water from artesian sources. All these factors, and probably
others as well, can affect the level of a lake and the discharge of
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 73
water through it, but the present report is concerned with these
matters only as they are indicative of the origin of the basin the
lake occupies.
As far as fluctuation of surface is concerned, the Florida lakes
fall readily into two major categories: those with surface outlets,
and those with underground or seepage discharge. A lake with
surface drainage maintains a rather uniform level of surface
which is largely controlled by the level of the spillway over which
it drains. If the basin of such a lake is the result of solution of
limestone by the water that has been discharged through the lake,
variations in the rate of discharge accelerate or decelerate the
process but probably do not change its nature.
As mentioned above, those large shallow lakes which are widely
fluctuant in level and do not have surface drainage appear to be
victims of a drop in the water table or the piezometric surface or
both. They seem to have had surface outlets and more stable
surface levels in former times, therefore their present vagaries of
regimen are probably a matter of little concern in the study of the
origin of their basins. The quixotic fluctuations in the regimen of
a "disappearing" lake seem to be the result of processes which are
destroying the lake rather than forming it.
Influence of Local Relief in Forming Lakes: Most of those lakes
which can be recognized as having developed around sinkholes,
either single or multiple, differ from most of the large surface-
drained lakes in that they are found in areas of locally high ground.
That is to say, they occur on ridges or uplands rather than in
valleys or lowlands. So in certain areas where old beach ridges or
other local highlands are discernible, small lakes appear in linear
groupings located in the tops of the ridges, rather than in the
swales between them.
Thus in Hillsborough and Pasco counties a low sandy ridge
extends northward from the city of Tampa, passing between
Sulphur Springs and Citrus Park, through Lutz, between Drexel
and Ehren, and east of Greenfield and Loyce. It is followed
generally by the part of the Seaboard Air Line Railroad which
runs from Tampa to Brooksville. This ridge averages about six
to eight miles in width and is some 20 to 40 feet higher than the
adjacent lowlands to the east and west. The upland surface of
the ridge is pocked with small lakes, the largest of which are one
or two miles in longest dimension. Among them are Egypt Lake,
White Trout Lake, Carol Lake, Ellen Lake, Lake Magdaline, and
Platt Lake, in the northern environs of Tampa. In the lowlands
74 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
adjacent to this ridge there is much swampland, but there are
hardly any lakes, whereas the upland surface between lakes on
the ridge is very well drained land.
As far as the writer knows, there is no lithologic or structural
difference between the rocks underlying the ridge and those
underlying the adjacent lowlands. The apparent reason for the
presence of lakes in the well drained upland and their absence in
the swampy lowlands is that the elevation of the sand-coated
ridgeland above the adjacent lowland has permitted the water
table to go below the general level of the ground surface. This
has promoted a lateral subterranean flow through the sand over
the underlying limestone with resulting solution of the latter and
subsidence of the sand to form the lakes. The exact locations of
the lakes may have been determined either by inequalities of the
limestone or by zones at arterial flow of water. In the adjacent
lowlands, on the other hand, the water table is so near the surface
that much of the terrain is swampy and the principal discharge of
water is surficial rather than subterranean. It is probably
significant in this connection that most of the swamps of the
lowlands interconnect to allow surface drainage, whereas most of
the lakes of the upland have no surface outlets.
In considering the above explanation of this group of lakes
one should bear in mind that they may be the result of solution in
calcareous sands or shell beds in the overburden itself. However,
even if this is true the lakes are still the result of local relief,
highly permeable surficial materials, and horizontal movement of
ground water at shallow depth.
Aligned Swampy Sinks Controlled by Beach Ridges: In eastern
Orange County parallel lines of shallow swampy sinks appear in
the swales between old beach ridges. They may be seen very readily
on the aerial photographs. Rarely is there any secondary lineation
of these sinks at angles with that produced by the beach ridges.
Hence it would seem evident, not only that the lineation is
produced primarily by beach ridges rather than fractures in the
bedrock, but also that the solution is taking place at the surface
of the limestone rather than within it. However, these aligned
sinks may have been produced within a permeable shell bed by
water moving laterally. Mr. Harry Peek, of the Ground Water
Branch of the U. S. Geological Survey, called the writer's attention
to a similar situation in Manatee County, south of Tampa Bay.
There aligned swampy sinks are being developed in the swales
between old beach ridges by solution of a thin (up to 25 feet thick)
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 75
sand-covered layer of shells which rests on the impermeable clays
of the Hawthorn formation.
In both the Orange County and Manatee County instances
secondary linear features parallel with the regional structural
lineaments are rare. Thus deep circulation along fractures would
appear to have been insignificant in forming these sinks and they
would appear to be another instance of solution basins formed by
water moving laterally over the surface of soluble rock.
Lakes Along the Terrace Scarp in Citrus and Levy Counties:
A spectacular correlation between the occurrence of lakes and the
presence of permeable sand cover over soluble limestone may be
seen in Levy County. There as Vernon (1951, p. 25) has observed:
"... the Wicomico Terrace is composed of a belt of sand developed along
the Wicomico shoreline, and a former submarine limestone shelf called
the Chiefland Limestone Plain. The sand belt is developed along the
western foot of the Tertiary Highland and Coharie-Okefenokee Sand
Ridge. It enters Citrus County along its eastern central margin and
trends northerly to the vicinity of Bronson, Levy County, where it
merges with fluviatile sediments deposited along the valley of the
Waccasassa River. The belt is about two miles wide for the most part,
but broadens in southern Citrus County and up the valley of the
Withlacoochee River."
On the aerial photographs this sand belt is easily picked out at
the foot of a scarp which stands out very graphically, and it will
immediately be noted that this same sand belt is the location of
most of the lakes of this area. They are closely spaced in the sand-
covered zone with increasing incidence toward the foot of the scarp.
Some of the larger of these lakes resemble fault-dammed lakes in
that they finger out in ramifying apophyses and small ponds to
the westward away from the scarp, but become broad expanses of
open water toward the foot of the scarp. In many instances the
eastern shore, along the foot of the scarp, is nearly straight,
resembling the straight shore of a fault-dammed lake where it
borders the fault trace. These characteristics may be seen readily
in Johnson Pond about one and one-half miles south of the town
of Bronson, which is located at the junction of U. S. Highway 19
and State Highway 24.
This concentration of lakes in the narrow belt of sand-covered
limestone and their rarity in adjacent areas of relatively bare
limestone, attests the influence of the sand in the development of
lakes. Moreover, the increasing concentration of lakes with closer
proximity to the foot of the scarp, supports the idea that the sand
is influential in making lakes because the ground water moves
76 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
through it laterally. The water table would be steeply inclined in
the scarp and would be close to the surface of the ground at its foot;
the cover is thinnest there and it is there that the greatest
concentration of lakes attests the greatest solution beneath the sand
cover.
Lakes in the Periphery of the Chiefland Limestone Plain:
Another instance of the influence of sand cover and horizontal
movement of ground water as agents in the formation of lakes can
be found in the zone of small lakes and ponds which is peripheral
to the Chiefland Limestone Plain on its northeastern and south-
eastern sides between Long Pond, in Levy County, and the Gilchrist
County line.
The Chiefland Limestone Plain has little sand cover. It
comprises essentially a large outcrop area of limestones of the
Ocala group. It shows sinks and artesian springs, but no lakes.
Around the edge of this area the ground level falls off from an
elevation of some 40 to 80 feet (the elevation of the Chiefland
Limestone Plain) to the Pamlico alluvial surface at elevations of 40
feet or less. There is some considerable permeable insoluble cover
over the limestone at the edge of the Pamlico surface where it abuts
the higher surface of the Chiefland Limestone Plain. It is in this
insoluble sand cover that the peripheral lakes and ponds occur.
They are small, but closely spaced. In the adjacent areas there are
very few lakes.
Here again, as in the sand belt at the foot of the terrace scarp
farther east, the presence of permeable insoluble cover over soluble
bedrock located at the foot of a slope has facilitated solution of the
underlying limestone by horizontal movement of ground water
and has produced lakes.
Long Pond, the larger lake at the southwestern end of the group
of lakes in question here, no doubt owes its existence in large
measure to structural control of ground water discharge by the
Long Pond fault (Vernon, 1951). However, it probably would
have been a swampy depression rather than a lake had it not been
for the sand cover and the difference in elevation between the
Chiefland (Wicomico) and Pamlico surfaces.
Lakes Along the Lake Wales Ridge: In Polk and Highlands
counties, an elongate group of closely spaced lakes follows the top
of the Lake Wales Ridge. These lakes usually occupy prominent
depressions in the surface of the upland and frequently have high
steeply sloping rims quite unlike those of the large shallow lakes
of the lowland east of the ridge. Lakes are sparsely distributed to
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 77
the west of the ridge and the few that do occur there show little
resemblance to those found in the top of the ridge.
The many lakes in the top of the Lake Wales Ridge seem to
result directly from the relief of the ridge above the immediately
surrounding area. The marked difference in elevation between
closely adjacent areas promotes downward movement of ground
water and allows solution depressions to deepen themselves well
below the water table. However, one should bear in mind that
the water surface of most of these lakes is at the piezometric
surface. Many of them may have been localized by ancestral events
involving reactivation of solution features inherited from former
karst cycles developed before the last marine submergence. This
matter is discussed further below under the heading "Influence of
Deep Circulation."
Lakeless Limestone Regions-The Everglades: That the broad
shallow lakes are produced by solution from laterally moving waters
rather than by water moving vertically to deep circulation is
suggested by the fact that all such lakes are in areas where the
limestone bedrock is overlain by an insoluble cover, while the
Everglades, the only large area in which limestone lies bare at the
surface of the ground, has no lakes at all despite the fact that the
piezometric surface is above the surface of the ground. Other
smaller areas of exposed limestone such as the Chiefland Limestone
Plain are also lakeless.
The insoluble sand which forms the common cover on the
limestone throughout most of peninsular Florida, extends as far
southeast as the large shallow lakes do and no farther. Lakes and
sand terminate together at the latitude of the southeast shore of
Lake Okeechobee. Thus the Hillsborough lakes lie northeast of Lake
Okeechobee. Lake Hicpochee and Lake Trafford lie southwest of
it, all within the sand blanketed area, but southeast of the line
connecting these terminal lakes no lakes are found.
As shown by the contour map of the limestone surface
underlying the Everglades (fig. 8) tectonic features are reflected
in the limestone surface exposed in the Everglades, and as discussed
elsewhere in this report, these features have served to determine
certain subsequent attributes of the Everglades drainage through
their effect upon differential solution. Yet no lakes have been
produced. Since such fractures are ordinarily considered to be
the most common avenues through which surface water passes to
deep circulation, it would seem instructive that solution working
along these fractures, where they are exposed without cover has
78 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
produced no lakes despite its manifestation in other subsequent
features of the drainage.
It may also be noted in this connection, that the large shallow
lakes immediately to the north of the Everglades, such as Lake
Okeechobee and the Lake Marion group reflect these same trends
of tectonic fractures in their directions of elongation and in the
orientation of certain rectilinear parts of their shorelines. But
,these lakes occur where the limestone which is broken by tectonic
fractures underlies a considerable cover of insoluble and permeable
sand.
This notable absence of lakes in the southern end of the
peninsula is a matter of much geomorphic interest, which may
have a bearing on the origin of the limestone plain which forms
the Everglades. The Everglades are a great streamless area where
under natural conditions the water table is at, or above, the surface
of the ground most of the time. The lowness and flatness of the
terrain assure a high water table. The lower areas which stand
continuously under water have developed a cover of peat or muck
from the remains of aquatic vegetation. The high spots which are
frequently above water under oxidizing conditions do not
accumulate peat and, therefore, tend to remain exposed as relatively
bare limestone. They are subject to greater solution than the low
places for the general drift of water over the surface comes directly
in contact with the bare limestone, whereas the low places of the
limestone surface do not come into contact with the drifting sheet
of surface water because of their protective cover of peat.
The exposed limestones are frequently very spongy in character
apparently because of the extensive solution they have undergone
from exposure to surface water. On the other hand, the buried
limestone beneath the impervious peat frequently has a hardened
crust. Mr. Victor E. Muse of the U.S. Corps of Engineers office in
a personal communication to the writer made the following
statement:
"We have made several special pumping tests around the Everglades
area. These tests were designed to investigate multiple layer aquifers. In
almost all cases, we find that the upper portion of the rock acts as a
blanket-that is, it is considerably less pervious than the underlying
limestones. This probably has some significance and could mean that
the top layer has been casehardened or indurated."
Thus there seems to be a tendency for the high spots on the
limestone surface to be lowered by solution while the low spots are
more or less stabilized by their protective cover. Such a differential
in the rate of reduction might become an effective vertical control
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 79
for erosion and a plain surface might well result from its continued
action. This may account for the beveled limestone plain which
forms the Everglades.
More to the point in the present discussion, however, is the
fact that such a mechanism would be a destroyer rather than a
maker of lakes, for the peat and muck tend to fill up depressions
at the same time that solution is reducing the high spots which
would have to be the divides between any lakes. As the high
spots are reduced they also probably accumulate a protective layer
of vegetation, muck and peat, and the entire surface tends to pass
from one of topographic reduction to aggradation by universal
accumulation of vegetal remains. In the end there would be no
limestone exposed anywhere throughout the affected area.
In situations where there is no sand cover and water tables
as well as the piezometric surface are high there is little chance
to develop undrained depressions because of the "Everglades effect"
described above. If there is sand cover, however, and the water
table is high, movement of water may readily be through sand over
limestone, and the limestone can be reduced without the protection
offered by impermeable peats or mucks as in the Everglades. Such
underflows through sand could reduce the limestone at its buried
surface and let down the overlying insoluble sand to form the
lake basin. Vegetation would be unable to prevent this as in the
Everglades for the zone of water movement in contact with the
limestone would be subsurface through sand and therefore below
the wholly surficial zone of vegetal accumulation or peat develop-
ment.
Where water tables were low, of course, this idea would not
apply for the surface of the limestone would be dry and ground
water would move through openings of one kind or another within
the limestone itself. However, there might be a balance or
equilibrium of sorts in this situation also. For if the openings in
the limestone could transmit enough water to keep the water table
below the surface of the ground, they would probably also transmit
enough to drain any depression produced, and dry sinks rather
than lakes would result.
In correlating the large peninsular lakes with insoluble sand
cover over soluble bedrock, it would seem significant that the zone
in which they occur is in considerable measure coextensive with
the outcrop area of the Pliocene or Miocene sands and gravels
which are usually shown on the geological maps as the "Citronelle"
and (to a lesser extent) Alachua formations. In a considerable
part of this area ground water under artesian pressure passes
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through the limestone beneath the insoluble beds which are locally
rendered impermeable by a clay cement. It would seem plausible
that solution of limestone by such artesian water might bring
collapse of the overlying sands and cause lake basins to be formed.
Comparison of Florida Lake Country With Highland Karst
Elsewhere: Further suggestion that the large Florida lakes are
ipade by solution at the surface of the limestone may be had from
the fact that lakes are very common in this Florida karst region of
permeable sandy surface, but are not nearly as common or as large
in other karst country where the limestones are covered by the
tight residual clay soils produced by their own weathering.
High water tables must enter into this, but they in turn are
aided by the permeability of the sand cover because of its high
infiltration and negligible runoff. In regions of residual limestone
soil such as the Kentucky Karst Country or that of the Great
Valley, the surface runoff is high and the infiltration low by
comparison with the sandy Coastal Plain. There is little overland
flow into sinkholes in Florida, but rather seepage through the sand
which absorbs the rain as it falls and transmits it horizontally to
the sink underground.
In regions of tight residual limestone soils the water table is
low, not only because of relief, but also because of greater runoff
by overland flow directly to sinkholes and thence through caverns
to surface streams. Thus the dead zone of air-filled caverns prevents
the widespread development of lakes. But even in the valleys of
the lowest master streams of such regions there are few, if any,
lakes despite high water tables. This is probably a reflection of
greater surface erosion and mass wasting of clay soils which feeds
a large particulate load to the streams. The voluminous suspended
and bed load would tend to fill all solution depressions developed
along the streams and no lakes could develop.
Characteristics of Zone in Which Large Lakes Occur: The
larger lakes of the Florida Peninsula are limited to a rather sharply
defined area which has several peculiarities of shape and
orientation. As may be seen on the map shown in plate 1, this
area of large lakes begins rather abruptly at the north with Orange
and Levy lakes and terminates with equal abruptness in Lake
Okeechobee at the south. Its longest dimension is essentially parallel
with the axis of the peninsula and its western boundary parallels
very closely the principal reaches of sandy coast line on both
Atlantic and Gulf coasts. That is the section of the Gulf Coast
between Clearwater Beach and Sanibel Island, and the sections
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 81
of the Atlantic Coast between St. Augustine and Cape Canaveral,
and between Melbourne and Palm Beach. With equal nicety it
parallels the similar sandy coasts of the past which were formed
during interglacial times of higher sea level and are manifest now
in the many old beach ridges which are found at various elevations.
Significantly, this western boundary of the lake zone is located
at the Brooksville Ridge, the last beach ridge on the west flank of
the peninsula which was able to maintain a continuous supply line
of sand delivery from the mainland shores to the north (the
Coharie-Okefenokee Sand Ridge of Vernon, 1951). To the west
of this critical old beach ridge there is a much sparser supply of
sand for beach building, and veneers of sand overlying the limestone
bedrock are thin and really impersistent.
In describing the physiography of Citrus and Levy counties,
Vernon (1951) mentions the impersistence of the sand cover in
the west coast area as follows:
"Each [old] shoreline is marked by the development of a narrow belt of
sand along the coastal margins and further seaward by a broader belt
of limestone that has been planed by marine erosion to an irregular,
rolling shelf."
Thus to the west of the Brooksville Ridge there are only
narrow zones in which the limestone is covered to any appreciable
depth by permeable sand. For the most part, it either lies bare or
is covered by sediments which are usually too thin to support a
water table at or above its surface.
Vernon also calls attention to the fact that the conditions along
the present shoreline of the Gulf of Mexico are very similar to
those which prevailed along these older shorelines of Pamlico and
Wicomico time. And in contrasting the west coast of the Florida
Peninsula with its east coast, one of the most notable distinctions
is the paucity of beaches along the west coast compared with the
continuous broad beach of the east coast. It is well known that the
longshore currents of the Atlantic Coast sweep voluminous amounts
of sand southward along the beaches and keep them generously
supplied with sand. On the Gulf Coast, however, there seems to be
a significant lack, either of an adequate source of sand or an
adequate agent to transport it southward. Thus on the west coast,
beaches are found only between Anclote Key at the north and
Sanibel Island at the south. Elsewhere mangrove and marsh
dominate the indeterminate zone in which sea grades into land.
It is probably this sharp difference in sand supply between
east and west coasts which produces the straight western boundary
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of the zone of large lakes. The Brooksville Ridge which forms
this boundary has elevations reaching 220 feet above sea level.
This is probably high enough to assure that its eastern edge was
an Atlantic beach for there are no hills to the northeast of it which
attain this elevation, although subsidence by solution may have let
down higher areas to the east. The country to the east of this
sand ridge should be more consistently covered with sand because
most' of it has been passed over by Atlantic shores leaving a thick
and persistent veneer of beach sands.
This identity of the western side of the zone of large lakes with
the western side of the zone of thick persistent sand cover suggests
a genetic connection between sand cover and large lakes. However,
there are other factors which seem to have localized the big lakes
within this zone of sand cover. Chief among these is the structure
of Miocene sediments.
Relation of Large Lakes to Structural Highs in the Miocene
Sediments: Figure 10, which has been adapted from Vernon (1951)
shows isopachs of the Miocene sediments. It will be noted that
the lakes, except for a few developed in the Ocala group of lime-
stones, are found where the Miocene sediments are thin. The
thicker parts of the section are free of lakes. The areas in which
exceptional thicknesses of sediment are found are shown by four
prominent isopach highs: one in the northeastern part of the State
north of Gainesville; a second in Osceola County; a third in the
headwater area of the Alafia River, south of Lakeland in eastern
Hillsborough County and western Polk County; and a fourth in the
area of Tampa Bay. All of these areas are essentially without lakes.
The last two, of course, are outside the great zone of large lakes,
but they may well be the reason the lakes are absent nonetheless.
Most imperfections in the correlation between large lakes and
thin Miocene sections can be accounted for by generalization in
the drawing of isopachs for lack of data. Thus in the Osceola
County area the isopachs are closely crowded along the
northwestern and eastern sides of the structure, a place where
well data were available, and in these same places the correlation
between large lakes and thin Miocene sections is excellent. On the
southern and western sides of the structure, however, no well data
were available and the isopachs are spread out in a generalized,
gentle gradient which may not be representative of the actual
situation.
The northwestern side of the Osceola structure is straight and
precipitous and it parallels closely a group of aligned lakes which
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 83
occur along a prominent lineament which is easily seen on the
aerial photographs. Listed from northeast to southwest the names
of these lakes are: Conlin, Gentry, Cypress, and Hatchineha. This
lineament appears to be the trace of the fault which truncates the
Kissimmee Faulted Flexture at its southeastern end (Vernon, 1951,
pl. 2).
Considering the relation between this linear group of lakes and
the abrupt termination of the Osceola structure on the northwest,
it would seem probable that there should be a somewhat similar
abrupt termination of the structure at the southwest. For an
equally prominent lineament is marked by an even more persistent
group of aligned lakes. These are oriented in a northwest-south-
east direction and listed in that order they are Lake Wilmington,
Lake Marion, Lake Jackson, Lake Kissimmee, Lake Hatchineha,
and a second Lake Marion.
Describing the isopachs, Vernon notes that the Miocene has a
relatively flat top but an irregular bottom. He also notes that the
lower and middle Miocene generally thins toward the Ocala uplift
and lies upon it, but the upper Miocene thickens over the structural
depressions in the lower and middle parts of the section to account
for the greater thickness in the four isopachous highs described
above.
Considering that the upper Miocene is generally less soluble
than the lower and middle Miocene, it would appear that the large
lakes have been formed where the sand cover overlies the more
soluble lower beds without thick insoluble beds of upper Miocene
intervening. However, much of the upper Miocene is sandy and it
may well be that it takes the role of the permeable cover through
which ground water moves laterally over the surface of the soluble
rock. If this is true, the dearth of lakes in the isopachous highs may
be because the surface of the underlying soluble bed is too far below
the water table to have much ground water flow or therefore
much solution.
Wasting of Lake Water: In addition to the sand cover and
availability of soluble bedrock, a third requisite to the formation
of large lakes would appear to be an effective means of wasting the
water that forms them. As mentioned above, voluminous solution
of limestone demands voluminous discharge of water over its
surface. Therefore, within the limitations of the factors already
described-sand cover and soluble bedrock-an outlet for the water
of the lake seems to be an additional requisite. Loss of water to
subterranean drainage is improbable because the large permanent
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lakes have surfaces lower than the piezometric surface. As the
lake becomes broader the ratio of surface area to shoreline length
increases and evaporation probably becomes a significant factor.
Nonetheless, most of the large peninsular lakes, as mentioned above,
are threaded along the major streams. A list of these lakes is given
above.
Other lakes seem to owe their existence to the disseminated
wasting of water through swampy draws. Voluminous discharges
can pass through such swampy draws without being noticed. Thus,
as described elsewhere in this report, a discharge approximating
500 cubic feet per second passes from the Withlacoochee River into
the Hillsborough River, through a swampy forest. Yet this leakage
was not suspected until a highway fill was built across the swamp,
forcing the disseminated discharge to concentrate itself into a
single stream where it passes through the opening under a bridge.
The large lakes of Leon County described by Sellards all have
occasional surface drainage and probably had perennial surface
drainage at the time they were formed.
Vernon (1951) postulated that Prairie Creek (which now drains
into a sink in the former disappearing Alachua Lake near
Gainesville) may formerly have been the headwaters of the
Wacassasa River, thus Alachua Lake would have had perennial
surface drainage when it was a perennial lake.
Relation of Lakes to Piezometric Surface: There is still another
geomorphic factor in the formation of the large lakes which is
quite as important as the sand cover. This is the fact that virtually
all the large shallow lakes have water surfaces well below the
piezometric surface. The only exceptions to this rule that the
writer knows of are the northernmost peninsular lakes, which are
in the general vicinity of Gainesville in southern Alachua County,
and northern Marion County. Here Orange, Levy, Ledford, and
Newnans lakes all have surfaces which are very close to the
piezometric surface. They seem to be in a transitional zone, between
the general region to the south, where all the large lakes are below
the piezometric surface and an area to the northwest where the
piezometric surface is lower than the surfaces of extinct large
lakes, such as the former Alachua Lake (the present Payne
Prairie), and the prairies such as Sanchez, Kanapaha, and
Hogtown, which give every indication of having once been large
shallow lakes.
This northern zone of former large lakes seems to be an area
where the piezometric surface has fallen. A strong suggestion of
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 85
this is offered by the famous "disappearing act" of Alachua Lake,
which at irregular intervals used to drain itself dry through
Alachua sink, a solution pipe in its northeastern rim (it is now
drained artificially by a ditch). This behavior, of course, could
have been produced merely by lowering the water table, quite aside
from any influence of the piezometric surface.
What is perhaps better evidence of a lowering of the piezometric
surface in this general region is offered by certain valleys which
are now dry, although they head at the sites of what appear to be
former artesian springs. Thus Stubbs (1940) observes:
"Many of these springs have developed channels and now form short
streams. The Itchatucknee River emptying into the Santa Fe River
just south of Hildreth is entirely a spring-fed river. Its head is
Itchatucknee Springs, the third largest measured spring in Florida.
All along the course of the stream, however, there are large and small
springs feeding into it. This river is probably the surface expression
of a longer underground stream. It has developed by a successive cutting
back through the formation of sinkholes and large springs along its
course. There is some evidence that at one time the Itchatucknee may
have extended farther north, and that this northward extension went
underground some distance above the present spring. If this is true
the drying up of this more northern stream may be accounted for by
a drop in the permanent artesian head of the waters in that area.
There is considerable evidence that such must have occurred in the
case of some short tributaries of the Santa Fe just west of High Springs.
There are two very distinct stream channels, now dry, in that area.
These were spring-fed and the old spring mouths are still clearly evident,
but the artesian head has now dropped too low for these springs to
flow."
Edwards (1948) also described one of these abandoned valleys
and spring heads in detail.
All this suggests that the present large shallow lakes can exist
only in localities where the piezometric surface is higher than the
area occupied by the lakes. The mechanism through which this
factor works to aid in forming these lakes seems to be that the
limestone underlying the sand cover is incapable of transmitting
ground water downward to deep circulation because the artesian
pressure directed upward from below prevents its entry. If any
vertical exchange of water takes place, it is in an upward direction
with artesian water leaking into the local ground water above the
aquifer. Thus if there can be no downward discharge of ground
water to deep circulation, the water table in this region of fairly
heavy rainfall must remain high and discharge must be by
horizontal movement. This horizontal flow takes place
fundamentally through the sand, and discharge is a regional drift
of water toward the lowest places in the land surface where the
few streams are found. In the process of this same horizontal
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movement through the sand, the drifting ground water dissolves
the upper surface of the more soluble limestones. This forms the
lake basins, and the high water table is able to keep them full of
water even though they are usually very shallow.
The fact that these lakes have surfaces below the piezometric
surface probably assures them of greater longevity than they
might otherwise have. Their water surfaces are not so subject to
the caprices of rainfall variation because if there is any artesian
leakage the piezometric surface, which is usually well above the
lake surface, must fall below it before the lake level can be much
affected. In other words, the piezometric surface must fall below
the water table before water table and lake level can fall
appreciably. Of course, this effect of artesian pressure in preventing
loss of deep percolation is made possible by the low relief of Florida
and the resulting high water tables. It could not exist if the
artesian aquifer were deeply buried beneath an impermeable cap
in a country of high relief.
Any longevity so acquired would doubtless aid in giving these
lakes their large size, for the solution process could operate over
a long period of time.
Summary: In summation of the factors which seem to influence
the development of large peninsular lakes it may be helpful to
repeat that large lakes are likely to be found:
1. Where sand cover overlies soluble limestone in thicknesses great
enough to maintain a water table in the sand most of the time.
2. East of a nearly straight line connecting the west shore of Lake
Tsala Apopka at the north with the west shore of Lake Hicpochee at
the south.
3. East of Brooksville Ridge.
4. In areas where beaches were formed by Atlantic waters rather than
by those of the Gulf of Mexico.
5. Along major surface streams.
6. Along structural lineaments.
7. In situations which assure voluminous discharge of water through
the lake.
8. In localities where the upper Miocene sediments are thin or in
structural highs of the Miocene.
9. In the areas covered by the "Citronelle" formation.
10. In areas where the piezometric surface lies at or above the land
surface.
Influence of Deep Circulation: Most of the discussion of the
origin-of the lakes described in the above section of this report has
centered around the idea of ground water moving horizontally
through permeable sands at shallow depth. However, one should
not lose sight of the fact that great volumes of water are discharged
from the peninsula through an apparent labyrinth of solution
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 87
openings in the underlying limestones. The great volume of this
artesian discharge is attested by the great many springs of the
peninsula, all of which seem to feed from deep open pipes in the
underlying limestone. Again the great discrepancy between
precipitation and the total discharge of surface streams indicates
the large percentage of the precipitation which is discharged
through deep artestian avenues.
In describing at length the apparent effects of shallow water
movements, the writer has not sought to neglect the great effects
of deeper circulation. But in the past it has been customary to
accredit all topographic effects of solution to deep circulation, and
the writer has sought only to show that many topographic effects
of solution are engendered by a circulation that is largely discrete
from that of the deep aquifer. Despite this classic tendency to
accredit all topographic solution to deep circulation, its topographic
effects are usually more inscrutable than those of the shallow
circulation described above.
For the most part, the karst features produced by circulation
within the bedrock are products of several cycles of subaerial
exposure. The karst topography of previous periods of emergence
has, in most instances, been buried by the sands deposited during
later interglacial times of high sea level. Because of the recurrent
nature of the glacial ice, many of these features may have been
through several cycles of alternate burial by marine sands during
interglacial stages and reactivation of karst features during
glacial stages. Needless to say, this tends to make these features
difficult to analyze or sometimes even to recognize.
A particular reason for inscrutability is the fact that glacial
stages were brief by comparison with interglacial stages. Therefore
the time available for reactivation of karst on the lower terraces,
at least, has not been as great as that available for its concealment
by marine sedimentation.
Conversely, in the higher parts of the peninsula emergence may
have been continuous since pre-Pleistocene time. In such areas
there should be less evidence of concealment by post-karst
sedimentation, and the problem should be simpler. In practice,
however, the karst of these higher areas is just as difficult to
analyze as that of the lower areas. Actually, there may be little
difference between them save in age, for in each instance the soluble
limestone is overlain by insoluble material-the lower areas by
Pleistocene terrace deposits, the highlands by the sands of the
"Citronelle" formation. Although the latter are locally quite
argillaceous, apparently they are permeable enough to transmit
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ground water in the same manner as the sands of the Pleistocene
which usually are cleaner.
The highlands of the Lake Wales area rise well above the level
of the highest known Pleistocene sea level, but the lakes which occur
in the parts of these highlands which are higher than the highest
Pleistocene terrace are little different in appearance from those
found at lower levels. This is because the sands of the "Citronelle"
cover, the highest parts and apparently the mechanics of lake
formation are the same, both in "Citronelle" sand alone or in
Pleistocene sand underlain by "Citronelle."
Nonetheless, the character of the lakes in these highlands of
considerable local relief, is quite different from the lakes in the
less dissected regions. They are quite generally found in the
bottoms of depressions which have steep subaerial sides descending
many tens of feet below the level of the surrounding terrain. The
reason for these deep basins is obscure. In the absence of
Pleistocene sand on the highest uplands surrounding them, it
would seem implausible that they were once deep sinks which have
been partially filled with marine sediment.
When one considers (1) that these deep basin lakes are found
only on relatively narrow highlands like the Lake Wales and
Orlando ridges, (2) that they occur on such ridges, regardless of
the possibility of Pleistocene marine sedimentary fill, (3) that they
do not occur in any lowland area or in any broad, flat, reliefless
upland, and (4) that their water surfaces are at the piezometric
surface, one is tempted to suggest that they owe their existence
more to lateral movement of ground water from highland to
adjacent lowland than vertical movement from lake to deep aquifer.
The fact that many of these lakes drain through surface streams
tends to support this idea also.
On the other hand occasionally bits of evidence come to light
which suggest long, vertical connections between such basins and
deep artesian circulation. Thus Stubbs (1940) observes:
"The lake region of Polk and Highlands Counties is similar to that of
Orange, Lake and Seminole Counties, but here the covering of sandy
materials is greater and the sinkholes seem to be much deeper. Some
of these sinks extend to almost incredible depths below the surface. In
one well drilled just north of Haines City, casing was carried to a depth
of 900 feet without penetrating limestone. Ordinarily the wells in that
area have less than 400 feet of casing. The ground elevation at the well
probably does not exceed 175 feet. The sinkhole, therefore, extends to
at least 725 feet below sea level and perhaps to a much greater depth."
However, the presence of these deep sand-filled sinks does not
assure that ground water now passes vertically downward through
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 89
them. Developed in a former karst cycle, they may now be inactive.
Again the presence of deep lakes of small area in the south-
western peninsula shows the influence of solution by deeply
descending water at some former time of lower sea level. Cooke
(1944) says of these:
". . Five sink-hole lakes have been discovered in southern Florida, all
west of the Everglades . Deep Lake in Collier County, Rocky Lake in
Hendry County, Still Lake in Lee County. ... Salt Spring and Little
Salt Spring in Sarasota County.
"Most accessible of these is Deep Lake in the Big Cypress Swamp about
10 miles north of the Tamiami Trail (U.S. Highway 94) and 200 yards
east of Florida Highway 164.
"Soundings made in April 1942 indicate that the greatest depth is 95 feet
below the water level which, at that time, stood about 2 feet below the
land surface. The contour map . shows Deep Lake to be a true sink
hole with walls that are vertical or overhanging down to variable depths
of 35 to 50 feet, below which the sides slope gradually to the deepest
part of the bottom. The average diameter is about 300 feet, and the
area is about 1.6 acres.
"Still Lake lies about 16 miles east and slightly south of Fort Myers.
Soundings made in May 1943 show that its general form is that of a
funnel, and that the greatest depth is 208 feet below the water surface,
which, at that time, stood about five feet below the land surface. This
depth occurs in a sort of eliptical drain or 'chimney' filled to about 170
feet with soft organic ooze. The diameters of the drain are about 20
and 40 feet. The floor of the lake deepens rather uniformly with a
gradually increasing slope to about 125 feet, then drops abruptly in
the drain or 'chimney.' The average diameter of this lake is about
600 feet, and the area is approximately 6.5 acres.
"Rocky Lake lies in the Big Cypress Swamp about 17 miles east of
Immokalee. It is nearly circular and has an average diameter of about
840 feet; its area is about 12.7 acres. [Since this quotation was written
the depth has been found to be about 40 feet by the U.S. Geological
Survey.]
"Salt Spring, in Sarasota County, is about 7% miles northwest of
Murdock, and Little Salt Spring is 1.9 miles northeast of Salt Spring.
Both springs yield saline waters. The greatest depth in Salt Spring,
when sounded in October 1942, was 167 feet. Its surface then stood
about 3 feet below the level of the land. The spring is almost circular;
its average diameter is about 250 feet; and its area is approximately
1.1 acres. Its floor slopes gently out to about 40 feet from shore, then
drops abruptly to about 40 feet, where a shoulder 6 to 30 feet in width
slopes to a depth of 50 or 60 feet, then falls precipitously to the bottom.
"Little Salt Spring has not been sounded. It is almost circular, and is
estimated to be about the same size as Salt Spring."
The sediment-filled sink described by Stubbs must have been
excavated during a former period of emergence, for it has been
filled with marine sediments. The deep lakes and springs described
by Cooke would most plausibly have been formed during a former
emergence also, for they all bottom well below present sea level,
and the springs discharge salt water rather than fresh water. The
90 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
absence of sedimentary fill can readily be explained; as Cooke
observes, by the fact that very little sand is present in the area
where they occur. Nonetheless, the writer assumes there is some
meager possibility that the openings occupied by the springs could
have been dissolved out by the cold fairly dilute salt water which
discharges through them, and the lakes might possibly have been
formed by inverted syphoning of fresh ground water during the
present cycle.
Steep walled sinks of the northern peninsula, such as the Devil's
Mill Hopper in Alachua County, are more clearly products of the
present karst cycle, for they occur in a sand-covered area but have
no sand fillings.
Unlike the large shallow-basin lakes, the narrow deep-basin
lakes of the Lake Wales Ridge all stand approximately at the
piezometric surface, as nearly as the writer can determine from
available data. This would seem to be evidence that they are the
result of a circulation connected with the deep aquifer. But they
seem to encounter a considerable amount of recharge refusal from
the underlying aquifer. This is manifest in the fact that many of
them have surface drainage, via streams which follow broad,
structurally controlled valleys (cf. the Sebring, Lake Arbuckle,
Lake Arbuckle, S.W., and nearby sheets; see also the section of
this report which concerns the surface drainage of the Lake Wales
Ridge area). Thus it may well be that there is a considerable
horizontal flow of phreatic water into these lakes despite any
connection they may have with the deep circulation system. This
may explain the funnel-shaped cross section many of them have.
None of these lakes seem to be perched on impermeable materials
and this probably explains the fact that they occupy the bottoms
of deep steep-walled basins. To the best of the writer's knowledge
none of them ever "disappear" as do the lakes of Leon County or
the former Alachua Lake near Gainesville.
SOME GEOMORPHIC FEATURES OF CENTRAL PENINSULAR FLORIDA 91
REFERENCES CITED
Bishop, Ernest W.
1956 Geology and ground-water resources of Highlands County,
Florida: Florida Geol. Survey Rept. Inv. 15.
Cooke, C. Wythe (see also Parker, Garald G.)
1939 Scenery of Florida interpreted by a geologist: Florida Geol.
Survey Bull. 17.
1945 Geology of Florida: Florida Geol. Survey Bull. 29.
Corps of Engineers, U. S. Army
Preliminary examination of Withlacoochee River, Florida, for
flood control: Unpublished report on file in Jacksonville office.
1950 Hillsboro River, Fla.: Eighty-first Congress, second session, House
Document no. 567.
Fenneman, Nevin M.
1938 Physiography of eastern United States: McGraw-Hill, New York,
691 p.
Gould, Howard R.
1955 (and Stewart, Robert H.) Continental terrace sediments in the
northeastern Gulf of Mexico; Symposium on finding ancient
shorelines: Society of Economic Paleontologists and Mineralogists,
Tulsa, Special Paper 3.
Heath, Ralph C.
1954 (and Smith, Peter C.) Ground water resources of Pinellas
County, Florida: Florida Geol. Survey Rept. Inv. 12.
Leverett, Frank
1931 The Pensacola Terrace and associated beaches and bars in
Florida: Florida Geol. Survey Bull. 7.
Matson, George C.
1913 (and Sanford, Samuel) Geology and ground waters of Florida:
U. S. Geol. Survey Water-Supply Paper 319, 445 p.
MacNeil, F. Stearns
1949 Pleistocene shorelines in Florida and Georgia: U. S. Geol. Survey
Prof. Paper 221-F.
Parker, Garald G.
1944 (and Cooke, C. Wythe) Late Cenozoic geology of southern Florida,
with a discussion of the ground water: Florida Geol. Survey
Bull. 27.
Sanford, Samuel (see Matson, George C.)
Sellards, Elias Howard
1910 Some Florida lakes and lake basins: Florida Geol. Survey 3d
Ann. Rept., p. 43-76.
1916 Dead Lake of the Chipola River (abstract): Geol. Soc. America
Bull. 27, p. 109.
Shaler, Nathaniel Southgate
1890 The topography of Florida: Mus. Comp. Zool., vol. 16, p. 163.
Smith, Peter C. (see Heath, Ralph C.)
Stewart, Robert H. (see Gould, Howard R.)
Stubbs, Sydney A.
1940 Solution a dominant factor in the geomorphology of peninsular
Florida: Florida Acad. Sci. Proc., vol. 5.
Vernon, Robert O.
1942 Geology of Holmes and Washington counties, Florida: Florida
Geol. Survey Bull. 21.
1947 Cypress Domes: Science, vol. 105, no. 2717, 24 January.
1951 Geology of Citrus and Levy counties, Florida: Florida Geol.
Survey Bull. 33.
92 FLORIDA GEOLOGICAL SURVEY-BULLETIN FORTY-ONE
GLOSSARY OF GEOLOGICAL TERMS USED IN
THIS REPORT
Beach Ridge. A long, low sand ridge formed by waves and wind along the
shore of a coast exposed to the open sea. After sea level has dropped such
ridges mark the successive positions of the former coastlines and are
called relict beach ridges.
Consequent. A term used to describe the origin of a stream. It implies that
the present course of the stream is essentially the same as the one it had
when it came into existence. In most instances consequent streams follow
routes determined by the original low places in a terrain newly emerged
from beneath the sea.
Difluence. Flowing apart. A term used to describe a stream which branches
in a downstream direction.
Karst. Topography which has been shaped dominantly through the removal
of underlying rock by solution.
Lineament. An arrangement of topographic features along a straight line
revealing the presence of a fracture or other structural feature in the
underlying rock.
Offshore bar. A low sandy island formed by waves and currents in shallow
water. Usually highly elongate and parallel with the length of the coast.
Most of the present beaches of Florida are situated on offshore bars, Miami
Beach being a good example.
Phreatic water. Water in the ground below the water table, or in the zone
of saturation.
Piezometric surface. A surface marking the height to which artesian water
will rise under its own pressure in tightly cased wells.
Poccosin. An upland swamp. An area which maintains swampy conditions
despite an outward slope of the land. Because of low elevation, gentle
slope and interference offered to water flow by vegetation, the water table
rises to the surface of the ground and water is discharged in a slow moving
sheet which covers most of the surface.
Subsequent. The opposite of consequent. A subsequent stream is one which
has occupied its present valley by insinuating itself into an area of weak
easily eroded rock.
Vadose water. Water in the ground above the water table. It moistens but
does not saturate the ground.
Water table. The upper surface of the subterranean zone which is saturated
with water. The top of the zone of phreatic water.
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