THE PROBLEMS OF GEOLOGY 605 



of the causes suggested, we shall have some idea of their possible 

 relative importance. For my own part I have no doubt whatever 

 that volcanism is to be explained by some combination of the seven 

 causes mentioned, with doubtless other causes which have not yet 

 been suggested, rather than by a single cause. As soon as it is appre- 

 ciated that to explain a complex phenomenon several causes are 

 usual, if not invariable, rather than exceptional, it becomes plain 

 that their relative importance should be determiined, and this can be 

 done only by quantitative methods. 



THE INDIVIDUAL PROBLEMS OF GEOLOGY. 



Thus far we have been considering the problem of geology as a 

 general one. The subject assigned, "The Problems of Geology," 

 might imply a treatment of the particular problems at present being 

 considered by geologists. For an address this interpretation of the 

 subject is impracticable. Adequately to discuss one of the unsolved 

 problems of geology from the point of view advocated would require 

 a monograph. Not only is it impossible to discuss unsolved prob- 

 lems of geology, but it is impracticable, within the limits of this paper, 

 even to list the problems demanding solution. As evidence of the 

 correctness of this statement it may be noted that a subcommittee 

 of the Carnegie Institution stated scores of problems upon the inves- 

 tigation of rocks, the statement of which, limited to the briefest 

 possible terms, occupies a number of printed pages.' 



ILLUSTRATIONS OF TREATMENT OF GEOLOGICAL PROBLEMS FROM THE 

 POINT OF VIEW OF ENERGY, AGENT, AND PROCESS. 



While it is not practicable to discuss, or even to list, the particular 

 problems of geology, it is possible to mention illustrations of the sys- 

 tematization and simplification of the science by the treatment of 

 processes in terms of energy and agent. These I shall take from my 

 own publications, for the reason that I can more easily give them than 

 any others. My chief subjects of study have been (i) the gross and 

 minor deformations of the hthosphere, and (2) the interior trans- 

 formations of the rocks, or metamorphism. When I began the study 

 of the first of these subjects, I found a heterogeneous mass of facts 

 in reference to the deformation of many regions, with various guesses 



I Carnegie Institution Year-Book, No. 2, pp. 195-201. 



