SECOND ANNUAL REPORT—TOPOGRAPHY AND DRAINAGE. 
31 
As the coastal belt emerged from the sea by successive additions 
to its landward margin these streams gradually extended their chan¬ 
nels across this new land and hence became in part what is commonly 
known as extended streams. On the coastal belt they flow in broad, 
shallow trenches bordered by low banks of sand, and in some cases 
they have removed the Pleistocene sand and eroded channels in the 
underlying limestones and marls. The most important * extended 
streams of the State are the Escambia, Black Water, Yellow, Choc- 
tawhatchee, Apalachicola, Ocklocknee, Aucilla, Withlacoochee, Hills¬ 
boro, Peace and St. Marys Rivers. With the possible exception of 
the Escambia River all of these streams are in part superimposed upon 
the Pliocene or older geological formations. 
After the’deposition of the younger geological formations and the 
extension of the streams across the newly emerged land there came 
a slight Submergence which caused a shortening of the streams and 
permitted the sea water to enter the river channels for a distance of 
several miles from the coast. In this way the lower parts of the 
stream valleys have been transformed into estuaries which contain 
brackish water and are affected by the tides. The length of these 
estuaries or tidal portions of the rivers varies in the different 
streams, and even in a single river it may vary with the strength and 
direction of the wind. Strong on-shore winds raise the height of 
the water and force the sea water farther up-stream, while off-shore 
winds have an opposite effect. 
Lakes and Swamps:—Although the State of Florida is crossed by 
many large rivers there are numerous tracts of land which are very 
imperfectly drained and are occupied by lakes or swamps. The lake 
region will be more fully discussed on subsequent pages, and it is 
sufficient to note that lakes are very numerous, some of them being 
of considerable size. The swamps are of varying size, from a few 
rods to many miles in diameter. The most notable undrained area is 
in the southern part of the peninsula where the Everglades and ad¬ 
jacent lowlands form a nearly impenetrable wilderness. In this low¬ 
land tract lies Lake Okeechobee, which is one of the largest and most 
interesting lakes in the South Atlantic States. According to the 
measurements cited by Sanford the Everglades nowhere rise more 
than 22.4 feet above sea level, and the surface has 'such a gentle slope 
that the water which falls during the rainy season forms broad shal¬ 
low ponds and marshes which afford excellent opportunity for the 
growth of saw-grass and other aquatic plants. These plants by their 
partial decay under water have formed peat and muck deposits several 
feet in thickness. 
The smaller swamps and marshes occur in all parts of the State, 
but they are especially numerous in the belt of lowland which borders 
