MUSEUM OF COMPARATIVE ZOOLOGY. 149 
are only driven in the form of a thin sheet against the shore in the 
time of strong winds.. At other times, when winds are blowing from 
the westerly quadrant, the current is separated from the shore by a 
considerable interval of water which drifts from the north, and is much 
cooler than the Gulf waters. Probably the decrease in the growth of 
the reef north of Cape Florida is due also, in considerable measure, to 
the southward movement of sands along the beach. A very large 
amount of this sand is continually pouring around Cape Florida. The 
history of this migrating detritus appears to be as follows. During the 
glacial period, a very large amount of arenaceous material was con- 
tributed to the sea in the region north of Cape Hatteras. The general 
trend of the shore of this part of the continent is from the northeast to 
the southwest, while the prevailing direction of the wind is from the east. 
The result is, that so far as impelled by the waves, this sand works down 
along the coast shelf to the southward. Wherever it comes upon the 
beach and remains within control of the waves the southward movement 
is quite rapid. Coming upon the coral reef, this sand tends to bury the 
coral, and thus to limit its growth. North of Cape Florida, the sea-fans, 
or Gorgonias, which by their habit of growth are in a measure protected 
from movements of detritus, are the principal representatives of the 
polyps, the Manacinas occurring only as scattered-clumps amid a 
growth of the prevailing alcynoid polyps. North of Jupiter Inlet, the 
Gulf Stream departs yet farther from the shore, and it is unlikely that 
the temperatures are such as to favor the growth of a reef. The diffi- 
culties incident to my shipwreck near Hillsborough River made it im- 
possible for me to make more careful observations as to the condition 
of this reef. I am indebted to Mr. C. W. Coman, who was formerly 
keeper of the Lauderdale House of Refuge of the Government Life-say- 
ing System, for a great part of the facts which are here given. He 
has kindly followed my directions in observations on the extension of 
this reef. 
Imperfect as these observations are, they appear to me of interest 
from two points of view. In the first place, they add nearly one third 
to the known length of the living Florida Reef; and in the second place, 
_they show that while the reef may maintain itself for a certain distance 
beyond the constant influence of the Gulf Stream, the polyps cannot 
retain their full vitality when deprived of its current. 
There is reason to believe that the marginal reef of Eastern Florida, 
though it may now be extinct in the section north of Jupiter Inlet, has 
recently been somewhat developed even as far north as Mosquito Inlet. 
