THE BUILDING OF THE LAND 7 



snails with their beautiful shells and probably all 

 the region in which a majority of the native plants 

 have been derived from the Torrid Zone. It is 

 true that the flora of the seacoast littoral for a 

 considerable distance north of these two points 

 has been derived from Middle America, but, as I 

 show elsewhere, it is subject to occasional destruc- 

 tion by frost. A few very narrow strips of West 

 Indian trees and plants found immediately along 

 the beaches on dry land for some distance up the 

 peninsula owe their existence only to their im- 

 mediate proximity to the sea. 



During early or middle Pleistocene time (geo- 

 logically speaking, only yesterday) a considerable 

 subsidence took place throughout the peninsula 

 of Florida, and all the lower part of the State (to 

 north of the Caloosahatchee River) was sunk 

 below the level of the sea. Most of the rock of 

 the southern part of the State was formed under 

 water during this period of depression. If, by 

 any possibility, any of it had been above the 

 ocean before this time, the flora and fauna in- 

 habiting it were either drowned or driven to the 

 northward. The story of the building of the land, 

 so far as we need to trace it, may begin with 



