32 FLORIDA REEFS. 



to the Post-pliocene, and does not seem to have noticed that it is of coral 

 origin. The connection of these deposits with the Post-pliocene formations 

 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 hummocks, 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 these 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 



