206 L. V. Pirsson — Geology of Bermuda. Island. 



marine volcanoes. Provided that one believes in the perma- 

 nence of the deep ocean basins, it is clear that volcanoes situated 

 on their floors, after they had been cut clown to sea-level, if 

 they once projected above it, would be protected from further 

 erosion and avouM remain indefinitely as protuberant masses. 



Coral Island Platforms. — It appears to the writer that what 

 has been learned regarding the history of the Bermuda volcano 

 has an important bearing on the question of the way in which 

 the platforms on which coral islands, barrier reefs and atolls 

 are situated, have been formed. There is of course nothing 

 new in the idea that these may be volcanic in origin, only in 

 Bermuda we have once more a positive demonstration of the 

 fact. We have also seen that, provided the volcanic masses 

 are of sufficient antiquity, they may, even though of great size, 

 have been reduced to sea-level ; furnishing platforms of wide 

 extent. As mentioned above, such masses reduced to sea-level 

 would continue to project from the ocean abysses indefinitely 

 and many of them may be of great geologic age. There is 

 nothing in the mere size of any of the atolls of the Pacific 

 which would preclude their being placed on the stumps of 

 former volcanic masses ; it is not intended to assert by this 

 that the foundation in every case is necessarily a volcanic one. 

 If such masses have once been brought down to sea-level and 

 continue to exist and that level changes within limits from 

 time to time by warpings in different places of the sea floor, 

 or by an accumulation of ice on the lands and its melting, as 

 suggested by Daly,* then conditions of shallow water over 

 them may be established suitable for their colonization by those 

 organisms concerned in the production of the so-called coral 

 reefs, which may be formed under the conditions postulated 

 by Vaughan.f 



This paper will be followed by one dealing with the petrog- 

 raphy of the igneous rocks. 



Sheffield Scientific School of Yale University, 

 New Haven, Conn., April, 1914. 



* This Journal, vol. xxx, p. 297, 1910. 



f Jour. Wash. Acad. Sci., vol. iv, p. 26, 1914. 



