RELATIONS TO OTHER SCIENCES 613 



finally becomes a surface of maximum resistance. Plains of denuda- 

 tion (peneplains) seem to be such surfaces. The transformation of 

 the original surface into the surface of adjustment goes on much 

 more rapidly than does the reduction of the latter into surfaces of 

 denudation (peneplains) of maximum resistance. The original form 

 approaches the last form according to the law of asymptotes. For 

 this reason we do not find any plains of denudation actually ap- 

 pearing as perfect planes; they are only almost-plane, and appear as 

 peneplains. 



However rich in results for genetic morphology may have been the 

 observations of the forces at work on the earth's surface, this has 

 not sufficed to clear up our understanding of all these forms, for all 

 the forces at work are not visible at the earth's surface. Some act 

 too slowly, others, as glaciers, hide their processes from our observa- 

 tion. The analytical method of study of forms thus remains the only 

 available one. This method yields excellent results as soon as we 

 compare the forms with their contents, as soon as we bring them 

 into relation with the crust of the earth, and learn to compare the 

 surface features with the internal structure, or tectonic conditions. 

 In this case geomorphology is working upon a geological founda- 

 tion just as the topographer works from a geodetic foundation, 

 and where this necessary foundation is lacking, physiography must 

 supply it, just as in an unknown country it must also supply 

 geodetic work. Topography is often subordinated to geodesy in 

 civilized countries, and similarly there are cases where geomorpho- 

 logy is to be considered solely as a branch of geology. It is easy 

 to understand how those excellent investigators to whom we are 

 indebted for the first idea of the geological structure of the earth's 

 crust readily came to explain the earth's surface forms by the aid of 

 the knowledge they had already gained of its structure. As they 

 found evidences in the structure of the earth's crust of great dis- 

 locations apparently the result of violent forces, they thought that 

 the surface features of the land should also be explained by violent 

 crustal movements. It was long before students became emanci- 

 pated from this conception of violent catastrophes. It was long 

 before the idea became thoroughly incorporated that the forms of 

 the earth's surface are the results of the gradual and mutual reaction 

 of endogene and exogene processes. Even to-day wide differences 

 of opinion prevail as to the relative importance of each of these 

 classes of processes. The student of tectonic phenomena, who recog- 

 nizes in the stratigraphic structure of the earth's crust most magni- 

 ficent disturbances, finds so many cases where the external form has 

 been influenced by the internal structure, that he is inclined to 

 explain the physiognomy of the earth's surface as primarily the 

 result of the structure. The topographer, on the other hand, is 



