220 BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



semblance to an atoll," although they differ from one in several respects 

 which he enumerates. Dana and Sir Wyville Thomson regard the Ber- 

 mudas as part of an atoll. Thomson thought the islands were formed " by 

 the raising of the weather edge of the reef above the level of the sea." ' 

 Professor Eice also considered it an atoll, but he was careful to distin- 

 tinguish between the present outlines and those which belonged to the 

 original atoll. 



Professor Rice suggests the following heads as his explanation of the 

 geological history of the Bermudas : — 



" 1. A subsidence in which the original nucleus of the island disap- 

 peared beneath the sea, the characteristic atoll form was produced, and 

 the now elevated beach rock was deposited. 



" 2. An elevation in which the great lagoon and the various minor 

 lagoons were converted into dry land, and the vast accumulations of 

 wind-blown sand were formed which now constitute the most striking 

 peculiarity of the islands. 



" 3. A subsidence in which the soft drift rock around the shores suf- 

 fered extensive marine erosion and the shore platform and cliffs already 

 described were formed." 



As regards 1. This is the natural explanation which would be given 

 by the Darwinian theory of the formation of coral reefs to account both 

 for the disappearance of the original nucleus and for the formation of an 

 atoll. To those who do not accept the theory the disappearance of the 

 nucleus is of course explained by subsidence also, but by the subsidence 

 which followed the formation of the dunes from an extensive ring-shaped 

 coral sand beach of which the material was derived from a reef growing 

 upon the upper plateau of the Bermudian mountain, from a depth of less 

 than twenty fathoms. 



2. Whenever the accumulations from the reef were sufficient to 

 build up a beach reaching the surface, all the conditions necessary for 

 the formation of sand dunes existed, and we need not call upon either a 

 subsidence or an elevation to account for the existing condition of the 

 Bermudas. 



3. The subsidence which I imagine to have taken place after the 

 building of the dunes from the broad beach surrounding the original 

 nucleus — now sunk or disintegrated — is, it seems to me, quite suf- 

 ficient to explain the existing condition of the dunes and cliffs of the 

 Bermudas, if the interpretation I have given of the base rock is the 

 correct one. 



1 The Atlantic, I. 302. 



