AGASSIZ: THE FLORIDA ELEVATED REEF. 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," one can trace, proceeding 
southward, the gradual disconnection which has taken place between 
the Florida Keys and the maiuland proper, while between Key Largo 
and Key Biscayne they are still united with the mainland аб many 
points (Plate XIL), plainly indieating that they were a part of it after 
tho elevation of the coral reef. When we go farther west it becomes 
inore 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 Ху 
It is most probable that Key Biscayne Bay, Jard'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 theit 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 Arsenicker Keys. Similarly 
the Featherbed Bank and Black Ledge Bank (Plate XIII.) are the rem- 
nants of former strips of land, 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 Report of Mr, L. 8. Griswold on his examination of 
the southern extremity of Florida, page 52. 
