PHYSICAL HISTORY AND GEOLOGY. 39 



are to-day bringing about only annihilation. In order to trace 

 these changes it is first necessary to determine in how far the 

 present outline or area of the Bermudas is a permanent one, or 

 in how far it ma}' have varied during the period of its exist- 

 ence. By geologists, generally, the island group is considered 

 to represent the disrupted parts of an atoll-ring, most of which 

 (as is seen in the northern reef) now lies submerged beneath 

 the water. This is the view which is upheld by Dana in his 

 " Corals and Coral Islands " (p. 218) and by the late Sir 

 Wy ville Thomson in his work on " The Atlantic." The latter 

 states* that the character of the Bermuda atoll "is much the 

 same as that of like reefs in the Pacific, with certain peculiari- 

 ties depending upon the circumstance that it is the coral 

 island farthest from the equator, almost on the limit of the 

 region of reef-building corals." ' The atoll character of the 

 island group is also conceded by Prof Rice, but this authority 

 carefully distinguishes between the present outlines and 

 those which belonged to the original atoll ; he recognizes 

 movements of elevation and subsidence, which have practically 

 obliterated the normal form of the atoll, and have left it in a con- 

 dition where there need be no necessary correspondence exist- 

 ing between the present land-masses, with the submerged 

 reef, and the primary atpll-ring. The condition is thus stated 

 by him : " The series of movements required to account for 

 the main features of Bermudian geology seems to be the 

 following : 1. A subsidence, in which the original nucleus of 

 the islands disappeared beneath the sea, the characteristic atoll 

 form was produced, and the now elevated beach-rock was de- 

 posited. 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 

 sufifered extensive marine erosion, and the shore platform and 



*Op. cil., I, p. 302. 



