FLORIDA REEFS. 7 



prior to the formation of the outer reef the rising of which, as an external 

 barrier, must have modified greatly the course of the currents north of the 

 keys at a later period, leaving between them only a few narrow but naviga- 

 ble channels, such as exist now between the Marquesas and the Mangrove 

 Islands, between these and Key West, and between the Pine Islands and the 

 group of Bahia Honda. 



When describing in detail the different parts of the general reef, we shall 

 occasionally touch again upon different theoretical points only alluded to 

 thus far, and illustrate them more fully in their connection with the facts. 

 For the present a general idea of the topography will suffice. 



We would only add that the absence of corals along the western shore 

 of the peninsula, at present, is probably owing to the character which that 

 shore has assumed in the progress of time ; for the peninsula itself has once 

 been a reef, at least as far as the 28th degree of north latitude, as is sliown 

 by the investigation of the everglades, and by the examination of the rocks 

 at St. Augustine. 



This latitude is the natural northern limit of the formation of coral reefs, 

 as also of the extensive growth of stony corals, though on the southern 

 shores of the North American continent, these formations seem to have 

 extended far beyond their usual bounds, probably under the influence of the 

 high temperature of the Gulf Stream ; for not only do the narrow longitudi- 

 nal islnnds which extend along the eastern shore, and their direct connection 

 with the small keys north of Cape Florida, indicate their coralline origin, 

 but we have even under the 32d degree of north latitude extensive coral 

 formations at the Bermudas, still flourishing in the present day. If the 

 growth of corals has been stopped along the eastern shore, it must be 

 ascribed to the invasion of drift sand, which extends over the everglades, as 

 well as along the eastern shores as far south as the Miami, Key Biscayne, 

 and the bay of the Miami. 



Mode of Formation of the Reefs. 



The reefs of Florida, as they have been described in the foregoing sketch 

 of the topography of that State, and, indeed, the separate parts of each of 

 these reefs, in their extensive range from northeast to southwest, present 

 such varieties as will afford, when judiciously combined, a complete history 

 of the whole process of their formation. 



Here we have groups of living corals, beginning to expand at considera- 



