20 TRANSACTIONS OF THE [oCT. 13, 



reef at Nicols Town, Andros, and also that at Rose Island, near 

 Nassau. 



At Nicols Town the reef was about a quarter of a mile from 

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

 depth. Tiie reef was almost entirely composed of the great 

 Madreporapalmarum, with some small })atclie.s of M. cervicornus. 

 Both of these corals were growing luxuriantly, and their tips 

 were close to tlie surface of the receding waves. Tiie reef at 

 Rose Island, however, contained very few specimens of M. pal- 

 marnm, but many of M. cervicormis, 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 alcyo- 

 noid 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 Nicols Town, where the corals rose from the bottom. These 

 facts show, I think, that the Rose Island reef is an old one, while 

 the Nicols Town reef is in what we may call its prime. A study 

 of the chart of New Providence shows, running along its north- 

 ern 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 Oay, and Quarantine Cay have been formed. In other words, 

 I believe they have been formed in the same manner as L. Agas- 

 siz explained the formation of the cays of southeastern Florida. 

 He argues, however, that as the cays nearest the land, and hence 

 those lirst formed, are no higher than those farther seaward, it 

 follows that during their formation tlie land was stationary. 

 Prof. Heilprin,' on the other hand, has i)roved that the Florida 

 Peninsula is, or has lately been, rising. I think I have shown 

 that the Bahamas, or at least tiie islands of New Providence and 

 Andros, have very recently been rising; and yet,'although I have 

 no measurements, I venture to state that Salt Cay, the most sea- 

 ward one, is as high if not higher than Hog Island, that lies in- 

 side of it. 



To return to Florida. It would seem at first as if the conclu- 

 sions of Prof. Heilprin precluded the possibility of the cays be- 

 ing formed as suggested by Agassiz; for if we suppose a cay to 

 be formed while the land is rising, and then that another forms 



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



