BIGELOW. — SHOAL-WATEIt DEPOSITS OF THE BERMUDA BANKS. 581 



eiiteied but slightly into their formation ; a conclusion which is supported 

 by the composition of the modern sands. 



The oceanic character of Bermuda — its great distance from the 

 neighboring continent — prevents, as might be expected, its receiving 

 any important access of material from the continental slope, and conse- 

 quently its submarine deposits consist almost entirely of materials of 

 clearly local origin. The great scarcity of remains of pelagic organisms, 

 Globigerinae, Kadiolaria, Tteropoda, and the like, is a striking feature of 

 all the bottom samples examined ; and this is especially interesting in 

 connection with the results of our pelagic towing, from which we were 

 forced to conclude that the pelagic fauna of Bermuda, on the north side 

 of the islands at least, is very poor, both in species and individuals. On 

 the southern exposure of the bank the conditions might prove to be 

 different. But by far the greater area of the bank lies north of the 

 land crescent, which forms an effectual barrier against any surface cur- 

 rents which might be caused by the prevailing southerly winds. Castle 

 Harbor is the only sound to which water from the south has free access, 

 and it is interesting to note that several tropical pelagic organisms, 

 such as Velella, Charybdea, etc., have been taken here, but never on 

 the northern side of the islands, while some species of fish are also 

 known to occur only on the south shore. Shells of Spirula, however, 

 are found in considerable numbers on all of the beaches. The only 

 objects found which might possibly be of volcanic origin were a few 

 small particles of pumice. 



The great bulk, at least 90 per cent, of all the bottom deposits, what- 

 ever their nature, is composed of calcareous material. Siliceous materials 

 are exceedingly small in amount, and consist chiefly of the spicules of 

 various organisms, there being no siliceous particles of terrigenous origin. 



One of the most striking features of all the beaches and submerged 

 sands is the complete absence of any true coral sand, and the great rarity 

 of coral fragments of any kind. This is, of course, strictly in agreement 

 with the fact that the Bermudas are in no sense a coral island, and that 

 corul has had practically nothing to do with their formation and growth. 

 Corals, of course, flourish on the reefs, but form merely a thin incrusta- 

 tion over the underlying aeolian ledges. That they do not enter more 

 largely into the sands is due chiefly to the character of the forms occur- 

 ring here. In all coral islands and coral reefs it is the madrepores which 

 are chiefly responsible for the formation of sand, these being delicate 

 and easily broken up. But here, as observed by Agassiz ('95, p. 235), 

 the corals are mostly gorgonians, which are of course of no importance in 



