THE FLORIDA KEYS 37 



northern part of this great ocean river and which 

 had been raised above the sea by the first Pleisto- 

 cene elevation. It extended from East and West 

 Bahia Honda Keys (on the east) to Key West or 

 possibly even further west, and from the Content, 

 Sawyer, Johnson's, Mud, West Harbor, and 

 Northwest Boca Chica Keys (on the north) to the 

 inner edge of the Hawk Channel (on the south). 

 While this large island was entire, and perhaps 

 even since that time, various animals and the seeds 

 of tropical plants were brought to it, largely by the 

 Gulf Stream; these became colonized and finally 

 generally distributed over it. At the time of the 

 second depression (during later Pleistocene) the 

 island subsided slightly, but not sufficiently 

 to drown out completely its dry-land life. Its 

 eastern end was lowered until the waters of the 

 Gulf of Mexico occasionally swept over the lower 

 portions during severe northers. I found sea 

 shells of existing species scattered abundantly 

 along the southwest shore of Big Pine Key at a 

 height of about three feet above tide, and these 

 probably marked the extent of the greatest de- 

 pression. The water which was driven across 

 the low land scoured out a series of parallel chan- 



