PHYSIOGRAPHIC PROBLEMS OF TODAY 535 



produced; namely, diastrophic, plutonic, and volcanic physiographic 

 features. Each of the groups presents many as yet unsolved problems. 



Diastrophic features. — Under this perhaps unwelcome term are 

 included a large class of elevations, depressions, corrugations, faults, 

 etc., in the surface portion of the hthosphere due to movements within 

 its mass. The causes of the changes which produced these results 

 are as yet obscure, and, although a fruitful source of more or less 

 romantic hypotheses, may in general terms be referred to the effects 

 of the cooHng and consequent shrinking of a heated globe, or^vmder 

 the terms of the planetesimal hypothesis, reckoned in part among 

 the results of gravitational condensation. However obscure the 

 fundamental cause, the results in view are real, and among the larger 

 of the earth's features with which the physiographer deals. They 

 are the greater of the quarry blocks, so to speak, which have been 

 wrought by denuding agencies into an infinite variety of sculptured 

 forms. Included in the list, as the evidence in hand seems to indicate, 

 are continental platforms, oceanic basins, corrugated and block 

 mountains, and many less mighty elements in the marvelously varied 

 surface of the lithosphere. Not only the study of the shapes of these 

 features of the earth's surface, but the movements they are still experi- 

 encing, and their transformations through the action of denuding 

 agencies, claim the attention of the physiographer. While it may be 

 said that the investigation of the method by which the primary relief 

 of the lithosphere have been produced, falls to the lot of the geologist 

 or the geophysicist, the physiographer is also interested in the many 

 profound problems involved. The geologist and physiographer here 

 find a common field for exploration, and can mutually assist each 

 other. The task of the physiographer is to describe and classify the 

 elements in the relief of the lithosphere due to diastrophic agencies, 

 discriminate them from deformations due to other causes, and restore 

 so far as practicable the forms that have been defaced by erosion. He 

 can in this way assist the geologist by presenting him with the results 

 of diastrophism free from accessories. With pure examples of the 

 forms produced, the geologist will be better able to discover the causes 

 and their mode of action, which have produced the observed results. 



Although much has been accomplished in the way of determining 

 which elements in the relief of the lithosphere are due to diastrophic 



