GRAVEL AS A RESISTANT ROCK 1 



JOHN LYON RICH 



Cornell University, Ithaca, N.Y. 



INTRODUCTION 



The thesis which this paper will endeavor to establish may be 

 stated as follows: Gravel, in its relation to the agencies of denudation, 

 is, under certain geological conditions, a highly resistant rock. To 

 these agencies it will, in general, offer greater resistance than ordinary 

 igneous or sedimentary rocks, with a few possible exceptions. On 

 the validity of this thesis hinge important deductions as to the 

 normal course of topographic development in cases where such gravel 

 plays a prominent part in the geological structure of a region. 



It is my purpose (i) to point out the theoretical reasons for the 

 resistant nature of gravel deposits; (2) to show from an actual 

 occurrence in nature that the gravels do behave as the theoretical 

 considerations would lead us to expect; and (3) to sketch, byway 

 of suggestion, the normal course of development of topography in a 

 region where alluvial fans of coarse material are accumulating at 

 the base of mountains. By way of suggestion there will be further 

 a brief application of the principles brought out to certain well- 

 known topographic features. 



Except for the descriptive portion of the paper, which will be 

 clearly distinguished, the article is an analytical study made mainly 

 for the purpose of determining the influence of certain types of rocks 

 upon the processes and rate of denudation, and of calling attention 

 to what appears to be a normal cycle of denudation and the topo- 

 graphic development of mountains in an arid region, and to a 

 lesser extent in a humid region as well. 



At the present time no attempt will be made to review exhaustively 

 the literature of the subject. 



1 Published by permission of the Director of the U.S. Geological Survey. 



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