AGASSIZ: THE FLORIDA ELEVATED REEF. 51 
bluffs between the patches and stretches of the old coral reef; or it has 
accumulated upon the top of patches and stretches of reef to form the 
higher keys, and this æolian rock has, little by little, either remained 
more or less mobile, or been solidified by rain or the action of sea spray, to 
form the hard ringing limestone of the main line of the Florida Keys. 
From what we now know of the thickness of the reef from the borings 
of the Artesian well at Key West, the now elevated reef must have 
grown at no great depth upon the shallow shores of the Postpliocene 
coast of Southern Florida. The greatest depth upon which it began to 
grow was probably considerably less than the greatest depth at which 
reef corals are known to thrive. It was upon bars and flats at 
moderate depths, less than twenty fathoms, or upon their flanks, that 
the Postpliocene coral reef of Florida originated, — bars and flats ex- 
tending from the edge of the outer reef of to-day probably far beyond 
the northern limit reached by Mr. Griswold in his exploration of the 
Everglades. Over the whole of this southern tract of the peninsula, 
wherever a coral sand beach was formed, æolian hills and dunes were 
blown consisting of coral sand oólite, or of coral sand more or less mixed 
with quartz sand, as we proceed northward and inland from Key Bis- 
eayne, These molian hills and dunes have, little by little, been solidi- 
fied into hard rock by the same agencies as those which changed into 
pitted and honeycombed limestones the stretches of æolian rock covering 
the land surfaces and sinks of the Bermudas, and the extensive areas of 
similar formation so characteristic of the Bahamas.’ The territory 
covered in Florida by modified aeolian rock within the range of the 
elevated reef and beyond it (see Plate XVII.) is not as extensive as 
the similar area of the Bahamas. In fact, it is of about the size of the 
Little Bahama Bank. But there is a marked difference between the 
two sides of the Florida Strait. In the Bahamas there has been a very 
marked subsidence since the formation of the wolian hills of that group, 
--а subsidence amounting perhaps to three hundred feet, while the 
elevated reef forming the substratum of the Florida Keys indicates 
a slight elevation since the formation of the жоПап rock of Southern 
Florida. 
Finally, it is upon the remnants of the old elevated reef that the 
present growing reef flourishes, forming, as it does in the Bahamas and 
Bermudas, a comparatively thin crust upon the underlying foundation 
rocks, which aro now known to be Pliocene, and which occur at a depth 
considerably less than that at which reef corals are known to grow. 
1 A. Agassiz, “The Bermudas and Bahamas," Bull. Mus. Comp. Zool., Vol. XXVI. 
