234 IN LOWER FLORIDA WILDS 



marked. The upper parts of the streams are ill 

 defined in the great swamp. Their lowest parts are 

 mere lagoons, ramifying among the mangroves. 



It has been asserted that within the lifetime 

 of our plants and animals the peninsula of Florida 

 was elevated until a land connection was estab- 

 lished with the Island of Cuba and that over this 

 land way much of our tropical life has migrated. 

 To form such a passageway it would have been 

 necessary to elevate the whole area three fourths 

 of a mile, and had the land remained at this level 

 long enough for any considerable migration our 

 streams would have eroded deep valleys in the 

 soft rock. The surface of the peninsula would 

 have been worn into a very irregular topography 

 and the valleys once occupied by the streams would 

 now be fiordlike inlets of great depth. As a 

 matter of fact the beds of our streams are com- 

 posed of Pleistocene deposits, and none of them 

 has ever been lowered below their present level. 

 An additional proof that Cuba and Florida have 

 never been connected since the present flora and 

 fauna have existed lies in the fact that Cuba with 

 a thousand species of land snails possesses one of 

 the richest moUusk faunas on earth. Had a land 



