196 The Field of Geology— McGee. 



though its economic importance is such that it cannot be aban- 

 doned and must even be tilled more deeply than ever as the years 

 go on, it may be questioned whether it is not exhausted to compar- 

 ative barrenness unless new and more fruitful methods are devised. 



The phenomena of degradation were brought into prominence 

 by Lyell, and have ever since maintained an important place in 

 geologic literature. Within the last decade, however, a novel and 

 important cognate idea has been developed: it is now perceived 

 that the processes of degradation are governed by definite laws and 

 leave a legible record of their operation in the configuration of the 

 surfaces upon which they have acted, and consequently that geo- 

 logic history can be interpreted from the hills produced by degrada- 

 tion as well as from the strata produced by deposition in contigu- 

 ous areas. This discovery, simple as it seems, marks an era in 

 the progress of geologic science, if not indeed the birth of a new 

 science. Already the subject of "geomorphology" as it is called 

 by the director of the national geologic survey, or "systematic 

 geography," as the physical geographer of Harvard proposes to 

 term it, has attracted much attention among the foremost students 

 of this country, and nearly as much abroad. Thus this field, al- 

 though long worked, is to-day one of the most promising in the 

 entire domain of geology. 



Those phenomena of extravasation which trench upon strati- 

 graphy, petrography, and mineralogy have been carefully studied 

 and their significance and formal relations set forth as clearly as 

 present classifications permit; but while the still more interesting 

 physical relations have long been under investigation in various 

 parts of the earth by a score of vulcanologists, the great problems 

 of vulcanism and seismism remain in large part unsolved. These 

 problems cannot, however, be separated from those of deformation, 

 and this field of research is thus narrowed, though it promises rich 

 reward to profound workers. 



By reason of the impetus given by early studies, petrography 

 and mineralogy have been carried well forward, and great progress 

 has been made in ascertaining the genesis and relations of the ele- 

 ments of the terrestrial crust. Various rocks and minerals have 

 been discovered in nearly all portions of the earth, their relations 

 to each other and to the arts have been comprehensively studied, 

 and elaborate systems of classification have been devised for them; 

 the ores have been tested and applied to the uses of man in all 



