38 FLORIDA STATE GEOLOGICAL, SURVEY. 
water emerges at the bottom of the bay a few feet below mean tide 
level. On the opposite side of the town is a small lake with no sur¬ 
face outlet and apparently occupying a sinkhole. Usually the flow of 
this spring is comparatively insignificant, but at times the discharge 
is enormous. Observations made upon the lake just before and after 
one of, these outbursts of the spring appear to show that the lake dis¬ 
charges water into the spring through some underground channel, 
for the surface of the lake is said to have been lowered several inches 
while the spring was flowing rapidly. 
Aside from the large springs mentioned above there are many 
others which yield quantities of water, and springs of moderate size 
are to be found in nearly all parts of the State. Some of the smaller 
springs are supplied with water from the superficial sands, but many 
of them derive their supplies from the limestones. 
NORTH AND WEST FLORIDA. 
In West Florida and in parts of peninsular and northern Florida, 
the surface configuration has been largely determined by the erosion 
of surface streams. However, sink-hole topography is common as 
far west as Walton County, and many of the depressions are occupied 
by small lakes. 
Erosion Features: — From Leon County westward the major 
streams cross the upland in wide level-floored valleys bordered by 
well-defined bluffs. The depth of these valleys is due to the erosive 
action and the width to the meandering of the streams. The valleys 
usually contain a deposit of sand and mud, which rises but little above 
the level of the streams and is partially overflowed when the rivers 
are high. 
The small streams of the uplands flow in narrow valleys having 
steep walls and high gradients. In most cases erosion has not ex¬ 
tended far from the main streams, and hence there are many com¬ 
paratively level areas which form the divides between the principal 
rivers. On approaching the rivers, the areas of level land become 
smaller and the number and depth of the valleys increase until the 
surface is largely reduced to steep slopes. It is also worthy of note 
that the amount of dissection which the upland has suffered increases 
toward the south. Thus the largest level tracts of upland are usually 
found near the northern line of the State. At its southern edge, the 
upland sometimes descends abruptly to the coastal belt which borders 
the Gulf of Mexico. In some cases, however, the transition to the 
coastal lowlands is by a gradual slope. 
Lakes:—The uplands are usually covered by a few feet of white 
Pleistocene sand which masks the minor inequalities of the erosion 
