xviii PRE FA TOR Y NO TE. 



regions, I concluded that shells, the smaller corals, etc., 

 decayed, and were dissolved, when not protected by the 

 deposition of sediment, and sediment could not accumulate 

 in the open ocean. Certainly, shells, etc., were in several 

 places completely rotten, and crumbled into mud between my 

 fingers ; but you will know well whether this is in any degree 

 common. I have expressly said that a bank at the proper 

 depth would give rise to an atoll, which could not be distin- 

 guished from one formed during subsidence. I can, however, 

 hardly believe in the former presence of as many banks (there 

 having been no subsidence) as there are atolls in the great 

 oceans, within a reasonable depth, on which minute oceanic 

 organisms could have accumulated to the thickness of many 

 hundred feet. . . . Pray forgive me for troubling you at such 

 length, but it has occurred [to me] that you might be disposed 

 to give, after your wide experience, your judgment. If I am 

 wrong, the sooner I am knocked on the head and annihilated 

 so much the better. It still seems to me a marvellous thing 

 that there should not have been much, and long continued 

 subsidence in the beds of the great oceans. I wish that 

 some doubly rich millionaire would take it into his head to 

 have borings made in some of the Pacific and Indian atolls, 

 and bring home cores for slicing from a depth of 500 or 600 

 feet.' 



Stimulated, perhaps, by this letter from Darwin, Agassiz went 

 to work on the Florida reefs, and, in the next year, published 

 a paper 1 which contained the gist of his researches. In this 

 paper, he considered that these reefs could not be explained 

 by the theory of subsidence ; but that the polypes have grown, 

 under the most favourable conditions of food, temperature, and 

 oceanic currents, on banks which have been brought into their 

 bathymetrical zone by the accumulation of calcareous detritus. 

 'This explanation,' he says, 'tested as it has been by pene- 

 trating into the thickness of the beds underlying the coral-reefs, 



1 Mem. Amer. Acad. Arts and Set., vol. xi. p. 107; see also the 

 "Three Cruises of the Blake" {Bull. Mus, Comp. Zool. Harvard 

 Univ.) vol. xiv. iSSS). 



