SECOND ANNUAL REPORT—TOPOGRAPHY AND DRAINAGE. 
37 
above. The natural bridge of the Chipola River was submerged at 
the time the field work was done in that vicinity, so that no observa¬ 
tions could be made. However, the broad valley of the river above 
the bridge indicates that the upper part of the Chipola River has been 
a surface stream for a long period. Since natural bridges in such 
rocks are not apt to endure for long periods it appears probable, that 
this one may also have been formed by the second method. 
Sand Dunes:—A large part of the surface of Florida is covered 
by a few feet of Pleistocene sand. In the Lake Region this sand has 
sometimes reduced the original inequalities of the surface. In other 
cases the formation of sand dunes and ridges has increased the top¬ 
ographic irregularities. However, the dunes and ridges are seldom 
more than a few feet in height, and hence their effect on the topog¬ 
raphy is not very marked. 
Springs: — The great development of underground drainage in 
many parts of the State has already been mentioned. Where the 
streams emerge from their subterranean channels they form* springs. 
It is impossible to make any exact estimate of the number of springs 
in the State, and it is perhaps sufficient to say that they are exceedingly 
numerous. They vary in size from mere seeps to springs which give 
rise to creeks and rivers large enough to float good-sized passenger 
and freight steamers. The best known and largest of these springs 
is the Silver Spring in Marion County, which gives rise to a large 
stream of remarkable clearness and beauty. The water emerges from 
the basin which probably attains a depth of at least thirty-five feet, 
and the stream. Silver Spring Run, that flows from this basin, has 
an average width of about fifty feet and a minimum depth in the 
center of the channel of more than nine feet. The water is so clear 
that it is possible to discern objects lying on the bottom and to observe 
the fish and other aquatic animals. Among the other large springs of 
the region are Wekiva Spring, in Orange County, the source of the 
river of the same name; Sulphur Spring, near Tampa; Suwanee 
Sulphur Spring, White Sulphur Spring, Blue Spring, near Juliette 
Station; Blue Spring, near Orange City Junction; Green Cove Spring, 
on the St. Johns; Wakulla Spring, near Tallahassee; Itchetucknee 
Spring, near Fort White; Poe Spring near High Springs; Crystal 
River Springs which give rise to the Crystal River ; Weekiwachee 
Spring, near Bayport, and Newland Spring, near Falmouth. All of 
these springs are well known and many of them are very large. They 
are supplied with water by the underlying limestone which is every¬ 
where so porous and cavernous that it yields large supplies. 
A spring at Tarpon Springs is worthy of special mention because 
it .appears to be in part supplied with water from a small lake. The 
