MUSEUM OF COMPARATIVE ZOOLOGY. 149 



are only driveu 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 ciu-rent 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 gi'owth. North of Cape Florida, the sea-fans, 

 or Gorgonias, which by their habit of growth ai"e in a measure protected 

 fi'om 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 iMr. C. W. Coman, who was formerly 

 keeper of the Lauderdale House of Eefuge of the Government Life-sav- 

 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 IMosquito Inlet. 



