AGASSIZ : BAHAMAS. 177 



free from corals, their surface being more or less disturbed by the action 

 of the trades, thus choking off the growth of any delicate marine forms. 

 This leaves out of notice the great number of banks of the Bahamas, 

 that of the west side of Florida, of the banks extending from Cape Sable 

 to the Tortugas, of the banks to the south of Cienfuegos, extending from 

 the Isle of Pines to Cape Cruz, and, finally, the bank to the eastward of 

 Porto Rico upon which rise the Virgin Islands. Corals flourish upon all 

 these banks ; they form fringing and barrier reefs, and in a few instances 

 atolls, such as Alacran, the Hogsty Reef, and the atolls of the Mosquito 

 Bank, which I have not, however, examined myself. We cannot assume 

 that corals are only to grow where the base has reached the proper 

 depth during a period of subsidence, while they are denied that privilege 

 where the right depth has been reached in a period of elevation. 



There is no greater distance between the elevated reef of the south 

 shore of Cuba and the fringing reef of parts of San Domingo and Ja- 

 maica than thei-e is between those of the north shore of Cuba and the 

 barrier reef of the Florida Keys. The time at which the reefs of differ- 

 ent areas in the West Indies were elevated need not necessarily have 

 been synchronous, nor should we expect this in a district where volcanic 

 agencies have been at work on so great a scale. This would go far 'to 

 account for the great diversity of coral reefs we meet with in the West 

 Indian district within comparatively short distances. 



In fact, what I have seen so far in my explorations of the coral 

 reefs of the West Indies would show that wherever coral reefs occur, 

 and of whatever shape, they form only a comparatively thin growth 

 upon the underlying base, and are not of great thickness. In Flor- 

 ida they rest upon the limestones which form the basis of the great 

 peninsula. On the Yucatan Bank they are underlain by a marine 

 limestone. In Cuba they abut upon the Tertiary limestones of its 

 shores. Along Honduras, the Mosquito Coast, and the north shore of 

 South America, they grow upon extensive banks or shoals, parts of the 

 shore plateau of the adjoining continent, where they find the proper 

 depth. 



Similarly, along the shores of the Greater Antilles they are found rising 

 from depths suitable to their growth upon the shore plateaus, as well 

 as upon the peaks and summits of submarine ranges which either 

 come to the surface or approach it. Round the Windward Islands 

 they thrive upon the banks which surround them. But in neither case 

 have they played any important part in the building up of the banks 

 or of the shore plateaus upon which they occur. Upon the Bahamas 



VOL. XXVI— NO. 1. 12 



