DISCUSSION AS TO ORIGIN 279 



izes that there are planetary processes within the earth's interior beyond 

 his power of solution. Geikie* confesses that 



11 not even a satisfactory solution of the problems of the upheavals and depressions 

 of the land has been given. When we consider the wide tracts over which terres- 

 trial movements are now taking place or have occurred in past times the explana- 

 tion of them must manifestly be sought in some far more widespread and generally 

 effective force in geological dynamics. The causes of upheaval and depression of 

 land must again be traced back mainly to consequences of the internal heat of the 

 earth." 



Thus it is that the results of the purely geological study of the outer 

 phenomena of vuleanism, the examination of volcanic craters and rocks, 

 notwithstanding their long years of research and the great value from 

 other points of view, so far as their contributions to knowledge of the 

 conditions of the earth's interior are concerned, are incomplete and 

 unsatisfactory, and science must turn to the physicist, the mathema- 

 tician, and the astronomer for aid in investigating the earth's interior. 



INADEQUATENESS OF CRUSTAL THEORIES IN EXPLAINING ERUPTIONS OF PELE 



Owing to the fact that the geologist's observations are limited to the 

 phenomena which he sees on the earth's surface, there has been a tend- 

 ency to explain all the phenomena of vuleanism by the obvious ex- 

 terior processes. These theories, with their multiplied of variations, 

 all try to associate volcanic phenomena with movements of the earth's 

 crust, and some of them limit the causes and phenomena of vuleanism 

 to a narrow zone of the earth's outer diameter. All hypotheses of this 

 class may be grouped under the head of crustal theories. 



The recent West Indian eruptions resulted in the attempted applica- 

 tion of many of these crustal theories to the incidents in that region, 

 and it was the writer's studies of the geology of the islands and the im- 

 possibility of fitting the facts to the theories that has led to the writing 

 of this paper. 



The various crustal theories differ in detail. The most popular and 

 generally accepted of them is that volcanoes represent extrusions of 

 gases and molten rock from the earth's subcrustal layers. Surface fis- 

 sures are supposed to permit the entrance of surfical waters to the melted 

 rock, creating an expansive force, which extrudes the material. Some 

 advocates even maintain that the causes of the molten condition them- 

 selves are crustal, involving the melting of the rock through crustal 

 movements. 



Some maintain that the source of heat may be the load of the crust; 

 others admit that it is the general heat of the earth, but require the in- 

 Jetting of surface waters to produce extrusion and explosion. Nearly all 



* Text-book of Geology. 



