THE BERMUDA BORING 567 



they had been cut down to sealevel, if the_y once projected above it, would 

 be protected from further erosion and would remain indefinitely as protu- 

 berant masses. ... If such masses have once been brought down to 

 sealevel and continue to exist, and that level [of the sea surface] 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 

 . . . 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. ... It appears to the writer that what has 

 been learned regarding the history of the Bermuda volcano has an impor- 

 tant bearing on the question of the way in which the platforms on which 

 coral islands, barrier reefs, and atolls are situated, have been formed. . . . 

 Provided the volcanic masses are of sufficient antiquity, they may, even 

 though of great size, have been reduced to sealevel, furnishing platforms 

 of wide extent. . . . Such masses . . . 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" (206). In a word, Wharton's theory of trun- 

 cated volcanic islands as atoll foundations is here revived, though Whar- 

 ton is not mentioned; the only significant addition is the assumption of 

 a rise of sealevel as a means of submerging the truncated island. 



The difficulty that I find in accepting Pirsson's conclusions arises 

 chiefly from the lack of consideration that has been given to alternate 

 hypotheses other than the one here adopted. In the first place, it must 

 be manifest that a single boring gives no sufficient proof that the volcanic 

 foundation of the Bermuda limestones is a level surface of marine trun- 

 cation. The foundation may evidently be a volcanic mountain top made 

 uneven by subaerial erosion, while weathered detritus was washed from it 

 and deposited on its flanks beneath sealevel; if so, it is very improbable 

 that a chance boring should strike the highest point: volcanic rock may 

 well underlie Bermuda at a less depth than 245 feet; until additional 

 borings are made, this possibility can not be excluded. Similarly, the as- 

 sumption that the island was formerly unprotected by reefs long enough 

 for its complete truncation by waves is not made necessary by any of the 

 facts announced ; the island may have been surrounded by reefs for a long 

 period, and whatever degradation it suffered may have been chiefly due to 

 subaerial erosion. A long-enduring stability of the island may, of course, 

 be postulated and the consequences of such stability may be deduced ; but 

 the instability of the island may also be postulated ; surely such instability 

 is not inconsistent with the permanence of ocean basins. Dana believed 



XLII — Bull. Geol. Soc. Am., Vol. 20, 1917 



