176 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



depth of two thousand fathoms. Has that atoll been formed by its sub- 

 sidence 1 If so, we should have a great oceanic depression in the vicinity 

 of the Bermudas. We know nothing of the hydrography which does not 

 indicate that the mass underlying the coral reefs rises abruptly from the 

 ocean floor ; as to what height it originally rose, we have no data. 



Examine next the submarine range of the Windward Islands, with its 

 varied depths, of which the islands beginuing at the Grenadines and 

 ending with Saba are the exposed summits. Note the gradual widening 

 of the bank as we go north, and finally reach its widest part, upon which 

 are situated islands of recent limestone which have risen from a compara- 

 tively shallow bank, while farther south the recent limestones are limited 

 to the Basse Terre of Guadeloupe, or to the fringing reefs of Martinique, 

 St. Vincent, Dominica, and the Grenadines. 



Isolated from the other islands in the line of the submerged chain, we 

 have Sombrero, a recent limestone island, while Bird Island and the 

 Barbados are the summits of two isolated banks, both of different 

 heights. Surely, we have in that submarine chain a sufficient variety 

 in the depths of the bauk to account for the irregular position of the 

 limestone deposits now going on, and a sufficient number of points 

 which have readied by elevation the depth necessary and favorable for 

 the growth of coral reefs. Some of the localities have been elevated 

 above that level, as Barbuda, Antigua, Anguilla, Barbados, and Basse 

 Terre. while at other points — as Martinique, St. Vincent, and the Gren- 

 adines — the fringing and barrier reefs are still in full activity. 



The Saba Bank, the bank upon which have risen Antigua and Bar- 

 buda, and the bank within which are found Anguilla and St. Barthol- 

 omew, are extensive shoals compared with the dry land of the island. 

 Upon the Mosquito Bank also numerous coral reefs are found, rising 

 from varying depths, similar to those of the Yucatan Bank. 



Between the Mosquito Bank and Jamaica are a number of banks 

 within the 100 fathom line, some of which, like those surrounding St. 

 Andrews or Old Providence and the Morant Cays, have come to the 

 surface ; while others again, like the Serrana, Rosalind, Serranilla, and 

 Pedro Banks, have not reached a depth at which corals can begin to 

 grow, or have sunk below it. This gives in such a limited district as 

 the Caribbean Sea proper a sufficient number of instances of subma- 

 rine banks reaching all possible levels, some of which are in local- 

 ities where corals have developed to form fringing or barrier reefs, 

 others where the corals are reduced to irregular patches, and others 

 where, the conditions for their growth not being favorable, the banks are 



