SECOND ANNUAL REPORT-TOPOGRAPHY AND DRAINAGE. 
35 
other the materials that slipped away, no longer being able to retain their pur¬ 
chase on the walls, their support below having been removed. 
If the 'bottom of the sink does not contain an opening, the water 
which accumulates after a rainfall will usually escape to the under¬ 
ground stream by seepage; but where the amount of rainfall is too 
great to be carried away in this manner, lakes or ponds accumulate. 
The level of the standing water in such cases fluctuates, rising after 
each rainfall and gradually sinking during dry weather. There are 
hundreds of lakes in Florida which appear to belong to this class. 
Some of the sinks have an opening in the bottom which connects di¬ 
rectly with the underground stream. Into these openings the surface 
streams plunge, carrying their loads of sediment and other debris. 
This sediment probably aids the underground stream in enlarging its 
channel by mechanical wear, but sometimes it accumulates in such 
quantities as partially or even wholly to close the passage. In such 
cases the surface water remains in the sink to form a lake. Ex¬ 
amples of open sinks receiving the discharge of surface streams are 
common, conspicuous among them being the sink of the Santa Fe 
River, the sink of the Chipola River, the Lake sink in Jefferson 
County and Alachua sink near Gainesville. Alachua sink is import¬ 
ant because it illustrates some of the changes through which sink¬ 
holes may pass. This sink receives the drainage of a large stream 
which crosses a prairie (Payne’s Prairie). In the early history of 
the State this region appears to have been in about the same condition 
as it is today. 1 Later, owing to the outlet becoming closed, 2 perhaps 
by logs and other rubbish thrown into the stream, a large lake formed 
in the depression. About 1891, the sink reopened and the basin was 
drained, effectually ending the steamboat traffic which had developed 
on the lake. 
In some parts of the caverns the water which enters through the 
openings in the limestone evaporates, leaving a deposit of calcium 
carbonate. By gradual accretion these deposits may form large pend¬ 
ants—stalactites—hanging from the roof or walls. When the water 
falls to the floor of the cavern and evaporates, it often forms projec¬ 
tions known as stalagmites. The deposits in caverns are frequently 
highly ornamental and form the chief attraction for visitors. 
Sometimes the underground streams form new passages and aban¬ 
don portions of their old channels. The abandoned channels are the 
caverns which are visited by travelers. In Florida, only a few cav¬ 
erns have been explored and none are reported to be highly orna¬ 
mented. The most important caverns which were noted during the 
1 Bartram, William, Travels, 1791, pp. 187 et seq. 
2 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey Bull. 84, 
1892, pp. 94-96. 
