36 
FLORIDA STATE GEOLOGICAL SURVEY. 
field work are located near Marianna, Ocala and Alachua. The one 
near Alachua is known as Warren cave and is said to be well worth 
visiting. 
Natural Bridges: — Where the underground stream emerges it 
forms a spring and as the roof of the cavern falls it leaves an open 
channel through which the spring drains to some surface stream. By 
a continuation of this process the underground stream is transformed 
into a surface stream. Where a segment of the roof of the under¬ 
ground channel remains after the parts above and below have fallen, 
a natural bridge results. In Florida natural bridges may also be 
Fig. 2. A D represents the bed of a stream flowing across limestone. The 
development of an underground channel from X to Y caused the stream to 
abandon its surface channel. 
formed in another manner. In text figure 2 A D represents a 
longitudinal section of a surface stream flowing toward D and hav¬ 
ing for its bed the limestone A B C D. A passage, X Y, formed by 
solution, may permit some of the river water to take a course through 
the underlying limestone. As this channel is gradually enlarged by 
solution and mechanical wear, more river water passes through it. 
Finally, the surface channel may be unoccupied except during high 
water, or if the underground passage is large enough the surface 
channel may be entirely abandoned. A surface channel may also be 
produced across a natural bridge whenever the underground passage 
is partially obstructed. 
There are many natural bridges in Florida, small ones being re¬ 
ported near Homosassa, north of Clarksville, in northern Walton 
County, and in many other localities. Large natural bridges occur 
on the Chipola River above Marianna, on the St. Marks River, south¬ 
east of Tallahassee, on the Santa Fe River, northeast of High Springs, 1 
and on several other rivers. The natural bridge on the Chipola River 
is submerged during high water, and a broad shallow surface channel 
which crosses the one near High Springs is said to carry a portion of 
the flood waters of the Santa Fe River. The breadth of the surface 
channel near High Springs suggests that the natural bridge of the 
Santa Fe River may have been formed by the second method outlined 
1 See Fig. 1, Plate viii. 
