PHYSIOGRAPHIC PROBLEMS OF TO-DAY 637 



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 has 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 

 agencies, only a small part of the difficulties to be overcome have been 

 met. The aim in view is the attaining of a knowledge of what would 

 have been the shape and surface features of the solid earth, had there 

 been no modifications by internal causes except diastrophism, and no 

 changes in relief by erosion or other surface agencies. Included in 

 this branch of physiography is the shape of the earth itself, in the 

 study of which the physiographer becomes a geodesist. The earth's 

 shape, and its primary surface features due to diastrophism, form the 

 logical basis for physiographic study, in which ideal types of topo- 

 graphic forms declare their usefulness. In the geographical museums 

 of the future, at the head of the long series of models of physiographic 

 types illustrating the species, genera, families, etc., of the earth's 

 surface features, should be placed ideal examples of the most typical 

 elements of relief due to diastrophism. 



Physiographers cannot rest content with the study of the shape of 

 the lithosphere and of its surface relief, in which so much of the his- 

 tory of the earth is recorded, and refrain from searching for the 

 deeper meanings these facts suggest, but must have freedom to invade 

 the province of the geologist, the astronomer, the physicist, the 

 chemist, and other subdivisions of the science of the cosmos, in search 

 of truths bearing on their special line of work. This is particularly 

 true in connection with the special department of physiography in 

 hand, in which many of the branches of the river of knowledge have 

 their sources. 



Plutonic Features. Intimately associated with the irregularities 

 of the earth's surface due to a decrease in its volume, and, as our 

 reasoning tells us, dependent primarily on the same cause and at 

 present only partially differentiated from them, are surface elevations 



