AGASSIZ: THE FLORIDA ELEVATED BEEF. 39 



(Plate XVI.) cannot fail to impress one with, the immense amount of 

 disintegration which has taken place there. Leaving out of considera- 

 tion the immense tract of lowland known as the Everglades, and con- 

 cerning which we as yet know so little, 1 one can trace, proceeding 

 southward, the gradual disconnection which has taken place between 

 the Florida Keys and the maiuland proper, while between Key Largo 

 aud Key Biscayne they are still united with the mainland at many 

 points (Plate XIL), plainly indicating that they were a part of it after 

 the elevatiou of the coral reef. When we go farther west it becomes 

 more and more difficult to trace this former connection until to the 

 northward of Key "West, between it and Cape Sable, the extensive 

 mud flats of the western part of the Bay of Florida, with here and there 

 an isolated mangrove islet or a half sunken sand-bar, are all that give 

 evidence of the former continuity of the land in the tract occupied by a 

 line drawn between these points. In the triangle formed by that line, 

 the keys, and the general line of the mainland from Cape Sable to Key 

 Biscayne Sound, the evidence of the former connection becomes clearer 

 and clearer in proportion as we proceed eastward (Plate XIL). 



It is most probable that Key Biscayne Bay, Card's Sound, Barnes 

 Sound, and the smaller sounds to the north of Key Largo, as well as a 

 number of ill defined sounds between Barnes Sound and the Bay of 

 Florida, owe their origin to the erosive and solvent action of the sea. A 

 glance at the chart clearly indicates the former connection with the 

 mainland of the line of keys extending from Key Biscayne to Long Key. 

 The nature of this former connection is perhaps best seen at the two 

 extremities of Key Biscayne Bay (Plate XIL). At its southern termi- 

 nation the tongues of land which divide Card's Sound into two basins 

 still exist, as well as the narrow disconnected strips separating it from 

 Barnes Sound on the south, while the dividing line between the north- 

 ern extremity of Card's Sound and Key Biscayne Bay is barely indi- 

 cated by the presence of the Rubicon and Arseuicker Keys. Similarly 

 the Featherbed Bank and Black Ledge Bank (Plate XIII.) are the rem- 

 nants of former strips of laud, extending from the Ragged Keys to the 

 mainland, which once divided Key Biscayne Bay itself into two or more 

 sounds similar to those forming Card's Sound. These sounds may 

 originally have been sinks similar to those of the Bermudas and Baha- 

 mas, and have, like those of these islands, been changed into sounds by 

 the breaking through of the barriers separating them from the open sea. 



1 See the accompanying Eeport of Mr. L. S. Griswold on his examination of 

 the southern extremity of Florida, page 52. 



