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 Baliia 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 shown 
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 islands 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 exten.sive 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. 
3Iode 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- 
