374 THE RELATIONS OF GEOLOGY. 



Again, every advance made by the geographical surveyor in the 

 accuracy and details of his maps has resulted in a corresponding 

 improvement in geological mapping and surveying. Ever}^ advance 

 made by the descriptive geographer in the discovery, delineation, and 

 description of the geographical relief of continental lands or of the 

 depths and deposits of the sea has increased geological knowledge, 

 and has stimulated geological inquir}^ and discover}^ in an almost cor- 

 responding ratio. 



But in this case of geography and geology, as in others, the ])enetits 

 have certainly been mutvial. Broadly speaking, almost the whole of 

 that vast mass of information which geographers now possess respect- 

 ing the work of those agencies which rule upon the djniamical side of 

 physical geograph}^ has been wrought out and accumulated b}^ geolo- 

 gists engaged in searching for the causes of geological action in the 

 past. The grand processes of denudation, erosion, and deposition; 

 the multifarious action of rain, rivers, and ice; the phenomena of 

 earthquakes and volcanoes, and the rock-making activities of animals 

 and plants were most of them first lal)oriously investigated by geolo- 

 gists, who welded them into tools for work in their own science and 

 then handed them over bodily for permanent lodgment in the well- 

 filled storehouse of the physical geographer. 



As regards the surface of the earth itself, so numberless of late 

 3'ears ha\e grown the visible and certain points of contact between 

 the phenomena previously regarded as proper to the one or the other 

 of the two sciences of geology and physical geography, and so evident 

 to all has become the sequence of geological causes and geographical 

 efl'ects, that many geographers have of late j^ears almost lost con- 

 sciousness even of the existence of a possible downward limit to their 

 science. Reveling in the wealth of geological facts and ideas already 

 accumulated and lying ready to their hand, scientific writers have 

 combined with their geographical description of the ''forms" of the 

 surface of the earth the geological explanation of their origins in that 

 most interesting branch of knowledge which is sometimes named 

 " geomorphology.'" This is undoubtedly a section of geonomic 

 science which is of great value, and is destined to grow in importance 

 as time goes on. But its stud}' presupposes a prelimiiuuy education 

 in which geology and geological causes take perhaps the largest share; 

 and those who would class it merely as a subscience of geography 

 are as wrong as those who class it merel}' as a subscience of geology. 

 It is the healthy and vigorous child of both. 



GEOLOGY AND PHYSICS. 



Here we enter upon more difficult and dubious ground, namely, the 

 relations of geology to the science of physics, especially in the matter 

 of the so-called "hypogene" agencies. The mechanical modes and 

 means of formation of our mineraloffical rock sheets have long since 



