PLANATION ACCOMPANIED BY LAND DEFORMATION 79 



ency for high mountain summits to approach the same elevation in a 

 given region after considerable lapse of time. It must be distinctly borne 

 in mind, however, that the process would not tend to produce broad, 

 level topped summits from very irregular masses. These high-level 

 planed surfaces might be confused with an uplifted peneplain or sub- 

 marine platform, which had been dissected to late maturity, so that there 

 were no broad areas of undissected upland ; but the details of form would 

 in nearly all cases be different. 



Too much care cannot be taken to see and carefully observe the topo- 

 graphic forms of dissected planed surfaces from the proper place to 

 bring out the continuity of the former plain. One should stand on the 

 edge of the yet undissected upland in order to look across ridge after 

 ridge of the summits approaching this level. The grades formed by the 

 later process of dissection here intersect the older and flatter grades of 

 the peneplain or plain of marine denudation. 



Planation in the Urals 

 evidence of subaerial degradation 



With a scheme such as that just described in mind, the writer studied 

 the Urals, and he came to the conclusion that it was highly probable that 

 the summit-level plane represents the action of subaerial degradation. 

 The continuit}^ of the uplands (plate 10, figure 1) and the accordance of 

 elevation of neighboring ridges are too great to have been the result of 

 abrasion of a continuously sinking land attacked from east and west, 

 and for the same reason the plane can not be the result of high-level 

 planation. 



The forms of the residual hard masses rising above the plane, as far 

 as seen, are typically the result of long continued land carving ; in other 

 words, they are monadnocks. 



The longitudinal drainage of the western slope of the Urals, particu- 

 larly that of the Kama and Ufa rivers and their branches, passing through 

 a few transverse courses, conforms so thoroughly to the structure that it 

 is thought to have originated from a system of drainage already well 

 adjusted when the subaerial planation of the mountains was completed 

 and the lowlands up-arched. It does not seem probable that such perfect 

 adjustment could result from streams consequent on a cover overlying 

 the planed surface. Marine i)lanation would then be out of the question, 

 and subaerial planation is the best working hypothesis for future studies. 



DISSECTION A T UFA 



Ufa, or Oufa according to the French spelling, lies at the junction of 



