32 FLORIDA REEFS. 
to the Post-pliocene, and does not seem to have noticed that it is of coral 
orio-in. The connection of these deposits with the Post-pliocene foi'inations 
of South Carolina, although it seems very probable, needs further proof; 
but a fact of greater importance, and one about which there can be no 
doubt, is, that the shore bluffs of the main-land are identical in structure and 
mode of formation with the subaerial deposits of the main keys. The lith- 
ology of the main-land is identical with the rocks of the keys as well as its 
mode of formation. Along the whole course of the main-land to the edge of 
the Everglades the appearance is the same. Indeed, a belt of coral rock, 
several miles in width, encircles the southern coast of the peninsula of 
Florida. This belt seems like a range of elongated hillocks, because it is 
broken here and there by cuts and depressions similar to those which sepa- 
rate the successive islands in the main range of keys. Within this belt, on 
the landward side, begin those inundated prairies known as Everglades. 
The bottom of these fresh- water swamps consists of the same muddy, semi- 
oolitic and concretionary limestone so characteristic of the northern shore of 
Key West, especially about the barracks. The bottom is very uneven, so 
that the sheet of water covering it varies in depth from a few inches to four 
or five feet, and in more extensive depressions forms shallow lakes. Where 
the ground is completely inundated, silicious sand covers it; but wherever 
the solid foundation rises to the surface, a soft soil is formed by the accumu- 
lation of decomposing vegetable matter. Such patches are here and there 
quite extensive, rising sometimes like islands one or two or even three feet 
above the shallow waters, and sustaining large trees and a rich vegetation. 
Such overgrown islands are called hitmmocks, and they make picturesque 
breaks in the otherwise monotonous flats of the Everglades. I have not yet 
ascertained by direct observation the extent of this formation in a northerly 
direction ; but Lieutenant Rodgers, who has crossed the Everglades in all 
directions, informs me that as far north as Lake Okeechobee, near the 27th 
degree of northern latitude, the character of the peninsula is the same as in 
those more southern portions which we visited together. Specimens from 
the shores of Lake Munroe, which I owe to the kindness of Count Pour- 
tales, satisfy me that the.se formations extend beyond the 29th degree of 
northern latitude. Even the Coralline in the neighborhood of St. Augus- 
tine, specimens of which have been furnished me by Lieutenant Rodgers, 
and by Captain Curtis, of Key West, must be, as I believe, the northern pro- 
longation of the same deposits. It is true that the rock there consists 
