44. BULLETIN: MUSEUM ОҒ COMPARATIVE ZOOLOGY. 
probably that of a line nearly 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 reof 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. None 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 
acrogs 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 Cæsar’s Creek the solian 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! states that Mr. Willcox found hard ringing жоПал limestone 
about ten miles inland, southeast of Punta Rassa, so that the northern 
limit of the æolian 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 a 
belt of more or less disconnected reef patches, separated by deep chan- 
nels, varying in width from two to three miles to more 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 solian sands. The depth of the channels 
1 Bull. U. S. Geol. Survey, No. 84, p. 101. 
