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 may 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 

 Wyville 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 atoll-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 is-lands. 3. 

 A subsidence, in which the soft drift-rock around the shores 

 suffered extensive marine erosion, and the shore platform and 



*Op. cit. y I, p. 302. 



