AGASSIZ: BAHAMAS. 173 



problem is a complicated one, and that we have not heard the last word 

 on the subject. As far as the formation of many of the Pacific atolls is 

 concerned, either they have been formed by subsidence, and owe their 

 origin to causes different from those which in the West Indian and 

 other districts have formed atolls upon comparatively shallow bases, or 

 they have been formed by the same causes to which the latter owe their 

 shape independently of subsidence, or we may further assume that atolls 

 can be formed in regions of subsidence independently of the subsidence, 

 as well as in regions where no subsidence has been observed. 



Darwin, and after him Langenbeck, as well as other writers on the West 

 Indian coral reefs, speak of the " extensive banks of sediment which have 

 been heaped up along the whole north coast of Cuba by sea currents." I 

 find it difficult to account for the origin of such a belief. That a great part 

 of the food supply of the animals living upon the banks has been brought 

 to them by sea currents is self-evident, but the mass, of sediment so con- 

 veyed is insignificant as compared with the accretions to the banks due 

 to the accunmlation and cementing of the carcasses of the Invertebrates 

 living upon them. There is, it is true, a long stretch of sand reefs and 

 islands all the way north from Key Biscayne to beyond Cape Hatteras, 

 but these have nothing in common with the limestone barriers forming 

 the basement of the Florida, Cuban, and other West Indian (Mexican 

 and Caribbean) coral reefs. 



I am surprised that Professors Dana and Bonney should both speak 

 so strongly against the statement of Murray, that there are known 

 numerous submarine elevations, mountains rising from the general level 

 of the ocean bed, which nfiay serve as the foundation of a coral reef. 

 Surely, we know as yet too little of the hydrography of the Pacific to 

 sweep away the statement with the suggestion " that such a thing may 

 occasionally occur." 



Professor Dana, who has made such a thorough examination of the 

 Feejee Islands, considers the conditions of the coral reefs of the islands 

 of the group as admirably illustrating Darwin's theory of the formation 

 of barrier reefs and of atolls. In spite of the general aspect of a sunken 

 continent made by the Feejee Archipelago, it is no proof that the reefs 

 owe their present condition to subsidence. It seems to me that the illus- 

 trations he brings up merely emphasize the great diversity of substruc- 

 ture of banks and islets and of large islands in the Feejee Islands 

 upon which fringing, barrier reefs or atolls might be found ; just as 

 in the Windward Islands and the Virgin Island Bank we find all pos- 

 sible conditions of elevation, from islets at the sea level, or sunken banks, 



