44: BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



probably that of a line Dearly parallel with the sea face of the main 

 line of keys, and about twenty or twenty-five miles inland. The reef 

 extended along a coast lower than the coast of to-day, and has been 

 elevated from six to twenty feet at certain* points, and the material 

 derived from the beach of this reef blown behind the reef has formed 

 the line of the keys, or the flats, and filled the sinks, extending far to 

 the northward. It is probable that the southern extremity of Florida 

 only rose to a limited height. ISone of the dunes are more than twenty 

 feet high, so that the work of erosion by the sea acted on an extensive 

 area, and there must soon have been many passages cut by the currents 

 across the present belt of the elevated reef and the adjoining land to 

 form the series of islands which characterize the inner waters of the 

 Florida Reef. 



If it were possible to distinguish in the material which goes to form 

 the bank off Caesar's Creek the seolian and the reef rock, we might de- 

 termine the extent of the coral reef, as well as that of the seolian ledges 

 which must have been thrown up along the former beach of the now 

 elevated coral reef. 



Dall 1 states that Mr. Willcox found hard ringing seolian limestone 

 about ten miles inland, southeast of Punta Eassa, so that the northern 

 limit of the seolian district, forming part of the great series of sinks be- 

 hind and within the limits of the elevated coral reef district of Florida, 

 may have extended as far north as that point. When discussing the 

 possible width and inland extension of the Florida reef in former times, 

 we have several factors to take into account. Perhaps the most impor- 

 tant one to limit the northern extension of the reef is the temperature 

 of the water; another, the amount of fresh water and silt which may 

 have been pouring out from the great sinks north of the reef; and finally, 

 the nature of the connection between the great reef patches which form 

 the belt of the Florida coral reef district. 



In Australia, at the present day, we have in the Great Barrier Reef «i 

 belt of more or less disconnected reef patches, separated by deep chan- 

 nels, varying in width from two to three miles to moi*e than seventy 

 miles. Some of the patches being many miles in length and in breadth. 

 The outlines of the patches which go to make up the belt of the Florida 

 elevated reef can only be traced here and there, so that it is difficult to 

 do more at present than to indicate, in a very general way the district 

 in which reef patches have been formed, or are likely to occur, but are 

 now covered perhaps by seolian sands. The depth of the channels 



i Bull. U. S. Geol. Survey, No. 84, p. 101. 



