50 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ment are by no means new. The principal reason for adding this paper 

 to the already overburdened literature on volcanoes is that it attempts 

 to coordinate the accepted principles of vulcanology with each other 

 and with the truths of plutonic geology. AVhether or not the actual 

 result is to meet with favor among geologists, the writer feels certain 

 that the synthetic ideal in vulcanological study has not been actively 

 pursued in anything like its just measure. That this pursuit necessa- 

 rily involves some speculation concerning the earth's interior is not a 

 valid objection to the undertaking. The earth's interior is no more 

 invisible than is the interior of a molecule. The sanction for modern 

 chemistry has become as strong as it is because philosophical chemists 

 have speculated about the invisible, intangible, and unweighable. 

 Similarly, to be more productive than it is, geology must become more 

 speculative. In this there is danger if the hypothesis is founded only 

 on the facts met with in the individual worker's experience ; there is 

 little danger, but great promise of fruit, if the speculation is synthetic 

 and regards all the published facts. 



During the preparation of this paper the writer has been greatly 

 aided by discussion of many points with his colleagues. Professor 

 W. C. Bray, T. A. Jaggar, Jr., G. N. Lewis, and A. A. Noyes of the 

 IMassachusetts Institute of Technology, and also with Professor H. N. 

 Davis, Professor L. S. Marks and Dr. P. W. Bridgman of Harvard Uni- 

 versity, and Professor A. C. Lane of Tufts College. To these gentlemen 

 the writer's sincere thanks are due ; he alone, however, must bear the 

 responsibility for the form and substance of the paper. He wishes 

 further to express special thanks to the Director and chemists of the 

 United States Geological Survey, who have supplied two of the chemical 

 analyses noted in the text ; to Mr. H. E. Wilson, of Hilea, Hawaii, 

 who has furnished one of the photographs here reproduced ; and to 

 Mr. Walter E. Wall, Government Surveyor of Hawaii, who has ex- 

 tended many courtesies to the writer, and gave him permission to copy 

 many manuscript maps used in the assembling of some of the facts on 

 which this paper is based. 



Abyssal Injection. 



Surveys on each of the continental plateaus have already shown that 

 the average rock of the plateau's basement (pre-Cambrian terrane) is, 

 chemically speaking, of granitic composition, with a silica-percentage 

 notfar from 70. Notwithstanding the vast erosions of many geological 

 periods, this terrane is, in places, known to extend downward several 

 kilometers even at the present time, and it is a reasonable inference, 

 contradicted by no fact yet discovered, that the acid complex has, gen- 



