44 NOTES ON THE GEOLOGY OF THE BAHAMAS 



Formation of the Cays north of New Providence 



The position, size, and shape of these larger cays have already been 

 noted. Before attempting to explain the manner in which I believe 

 they were formed, I will briefly describe the appearance of the reef 

 at Nicol's Town, Andros, and also that at Rose Island, near Nassau. 



At Nicol's Town the reef was about a quarter of a mile from the 

 shore, and the water varied from ten to eighteen feet in depth. The 

 reef was almost entirely composed of the great Madrepora palmarum, 

 with some small patches of M. cervicornus. Both of these corals were 

 growing luxuriantly, and their tips were close to the surface of the 

 receding waves. The reef at Rose Island, however, contained very 

 few specimens of M. palmarum, but many of M. cervicornus, and also 

 large heads of what are popularly known as "brain corals," but which 

 of the genera so designated I am unable to state. The receding waves 

 left the top of the reef bare, and exposed the sea fans and alcyonoid 

 corals that were growing on the top. Toward the shore the reef sloped 

 gradually downward into a bank of sand, or, in other words, the sandy 

 bottom sloped upward to the top of the reef, which thus presented a 

 very different appearance from the one at Nicol's Town, where the 

 corals rose from the bottom. These facts show, I think, that the Rose 

 Island reef is an old one, while the Nicol's Town reef is in what we may 

 call its prime. A study of the chart of New Providence shows, running 

 along its northern shore, a number of reefs, some of which are marked 

 nearly dry at low water. Now, in order to convert these reefs into land 

 it is only necessary that they should be slightly elevated or that sand 

 should be deposited on top of them. And this, I believe, is the way 

 in which the cays known as Hog Island, Rose Island, Salt Cay, and 

 Quarantine Cay have been formed. In other words, I believe they 

 have been formed in the same manner as L. Agassiz explained the 

 formation of the cays of southeastern Florida. He argues, however, 

 that as the cays nearest the land, and hence those first formed, are no 

 higher than those farther seaward, it follows that during their formation 

 the land was stationary. Professor Heilprin,^ on the other hand, has 

 proved that the Florida peninsula is, or has lately been, rising. I 

 think I have shown that the Bahamas, or at least the islands of New 

 ' Trans. Wagner Free Inst. Sci., Vol. I. 



