40 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



This would allow the gradual formation of more or less deep channels, 

 slowly increasing in width and in depth, through which material held in 

 suspension or solution could pass out and be deposited on the sea face 

 of the sounds, the sea encroaching upon the shores of the sinks forming 

 more and more distinct sounds, or even huge open bays like Key Biscayne 

 Bay, separated from the sea by a barrier of sand bores completely cover- 

 ing the eroded part of the elevated reef which once flanked the bay 

 from Key Biscayne westward, and of which Soldier Key, the Ragged 

 Keys, and Elliott Key are the remnants (Plate XIII.). 



Some of the larger and more extensive sinks characteristic of the 

 southern part of Florida may be due to folding occurring at the time 

 of the elevation of the reef forming the backbone of the larger Florida 

 Keys. Yet some of the sinks and sounds undoubtedly owe their origin, 

 not to the folding, as suggested by Mr. Griswold, but to the decomposi- 

 tion by water of the aeoliau rock deposited in the sinks, and to the 

 subsequent disintegration due to the carrying off of limestone, either in 

 solution or in suspension, through channels leading into open water. 



Key Biscayne, Virginia Key, Soldier Key, and the Bagged Keys remain 

 to attest the former existence of an extensive series of broad low keys, 

 the position of which is indicated by the wide and shallow bank that 

 separates Key Biscayne Bay from the waters of the Gulf Stream north 

 of Sands and Elliott Keys (Plate XIII.). The numerous deep channels 

 separating the banks to the westward of Key Biscayne undoubtedly 

 indicate the position of cuts similar to Bear Cut, which divides Virginia 

 Key from Key Biscayne. These keys have been eroded and the material 

 which forms the sand bores that cover the sunken surface of the ele- 

 vated reef has been brought by the currents from the low land which 

 once occupied the interior of the sounds. The meeting of the sea, due 

 to the prevailing winds, with the currents flowing out of Key Biscayne 

 Bay has resulted in the deposition of the material they carry, the 

 one on the sea face of that key, the other on the banks to the 

 southward. 



The spurs which extend in a northerly direction from the west side of 

 Key Largo (Plate XII.), some of which extend to the mainland, plainly 

 indicate the manner in which the line of keys lias gradually become dis- 

 connected from the peninsula of Florida. The western part of Card's 

 Sound is still separated from the sink of Barnes Sound by a continuous 

 strip of land, and further by a series of smaller secondary sounds which 

 will in time disappear with the erosion of the more or less disconnected 

 dividing laud .-trips. This will leave on that part of the Hats only Buch 



