580 PROCEEDINGS OF THE AMERICAN ACADEMY. 



millepores from the nearby ledges, with a few moUuscan and other 

 fragments. 



Hogfish Cut is the only one of the several channels penetrating the 

 boundary reef from which I have examined bottom samples. The col- 

 lection contains five of these, from as many localities between the cut 

 and the shore (Stations No. 430, 431, 434, 460, 461), which are almost 

 indistinguishable. They are very clean, fine shell sand, whitish, with a 

 faint pinkish tinge, with less than 1 per cent ooze. Although so clean, 

 the sand itself is as fine as the bottom at Nonsuch Scaur. Foraminifera 

 and their casts, especially Polystomella, form about 15 per cent; the re- 

 mainder consists of corallines, mollusks, millepores, corals, ostracods, 

 echinoderm remains, and Serjjula tubes. There are very few living or- 

 ganisms of any kind in this sand, which resembles sand from Nonsuch 

 Scaur so closely as to be almost indistinguishable from it. 



From the area of the bank outside the boundary reef, between.it and 

 the thirty-fathom line, I have, unfortunately, no samples, and my only 

 information is derived from the reports of fishermen and from what little 

 could be seen through the water glasses. The vigorous growth of corals, 

 gorgonians, millepores, etc., on the ocean faces of the reefs extends down 

 to only about six or seven fathoms. Here begins the " broken ground" 

 described by Agassiz (:95), as composed of various fragments and detritus 

 from the reef itself, together with great numbers of nullipores. At 

 about fifteen fathoms large sand patches appear, and in twenty fathoms 

 the bottom is chiefly sand (admiralty chart). 



General Considerations. 



The study of these samples of sand from the shoal lagoons of the 

 Bermuda Plateau is chiefly of interest for the light which it may throw 

 on the method of growth of a limestone island in a latitude where reef- 

 building corals are of but slight importance, and on the organisms chiefly 

 concerned in this growth. The Bermudas, from their superficial re- 

 semblence to an atoll, and from the fact that their reefs are largely 

 covered with corals, were considered as typical coral islands until the 

 time of Agassiz's visit in 1895. It is from this point of view that 

 Heilprin ('89) describes them, and Rein ('81) uses them as an example 

 of an atoll in combating Darwin's theory of subsidence. Agassiz ('95) 

 has, however, shown beyond possibility of doubt that this resemblance to 

 a coral formation is purely superficial, that their ring-like form is due, 

 not to coral growth, but to entirely different causes, and that coral lias 



