216 THE BERMUDA ISLANDS. 



ditional remarks are here necessary. In his more recent pub- 

 lication on the " Solomon Islands " Mr. Guppy informs us that 

 the tliickness of the coral limestone in the upraised reefs is in a 

 general way between 100 and 150 feet, and that he never found 

 a;i island " that exhibited a greater thickness of coral-lime- 

 stone than 150 feet or at the very outside 200 feet" (p. 71) 

 This is in itself an important observation, but it is just what 

 we should expect to find in a region of elevation, as we are in- 

 formed this one is. Without subsidence I fail to see how, on 

 the Darwinian hypothesis, a coral limestone could have a 

 greater thickness than 100-150 feet. The special significance 

 of the observation lies only in the fact that the same thickness 

 of coral-rock is associated with what is assumed to be a raised 

 atoll — namely, the island of Santa Anna. This island is de- 

 scribed as. being nearly circular in form, with a length and 

 breadth of two and a half and two miles respectively, and con- 

 sisting " of a central basin surrounded by an elevated rim [100 

 to 200 feet in height], which is wanting at the middle of the 

 west or lee side. The bottom of the basin, which extends 

 downward to about 100 feet below the sea-level, is occupied 

 by two fresh- water lakes," the largest of which measures about 

 half a mile in length, and has a depth of 18 fathoms in its 

 deepest portion. The highest elevation of the island, a vol- 

 canic peak, 470 feet in height, rises from the rim of the eastern 

 border, while another elevation, of 160 feet, is found in the 

 centre of the depressed basin. 



It does not appear clear that this is a true atoll ; and Mr. 

 Guppy himself admits that the island diff'ers " from the typical 

 reef of this description," although agreeing with the atoll-like 

 structures of the Solomon group ("Solomon Islands," p. 113). 

 It is manifestly a part of that class of structures, the horse-shoe 

 shaped reefs, which "do not assume their characteristic form 

 until they have reached the surface," and which the author 

 broadly distinguishes from the large atolls, which have proba- 

 bly " assumed their form beneath the surface " (Proc. Koyal Soc. 

 Edinburgh, 1885-86, p. 900). " A small flat-topped shoal is 



