CHAPTER XXI. 



THE PRINCIPLES OF GLYPTOGENESIS, OR THE SCULPTURING 

 OF THE EARTH'S SURFACE. 



During every geological period the complementary processes of 

 erosion and deposition were in evidence, sometimes the one pre- 

 dominating and sometimes the other. Deposition added material 

 to the crust locally, erosion removed it elsewhere. The results of 

 erosion in terms of form are the relief features, and the process 

 viewed from this angle is a process of sculpturing. The genesis of 

 land forms is thus in large part a genesis by sculpturing or gl\pto- 

 genesis."^ 



At all times, wherever land existed, erosion produced its charac- 

 teristic forms, controlled to a large degree by the character of the 

 material on which the forces of erosion were at work. Many of 

 the old erosion forms were buried beneath accumulations of new 

 rock material, and were thus preserved in a fossil form. Where 

 much deformation and alteration of the rocks has since occurred, 

 those older land forms may have become unrecognizable. Never- 

 theless, in many cases they are still in part preserved, and from a 

 study of modern types we may gain a sufficient insight into the order 

 of the development to enable us to reconstruct ancient examples 

 from partly preserved remains. 



The Cycle of Erosion. It is needful at the outset for us to 

 have a clear conception of the entire cycle of erosion as expressed 

 in land forms. Beginning with the young or newly formed land, 

 which may be a recently emerged coastal plain, a dome, anticline, 

 fault block, etc., the development of a drainage system as outlined 

 in Chapter III brings with it a progressive sculpturing and the pro- 

 duction of a series of topographic features, which carries the land- 

 scape through all stages of youthfulness to maturity and on toward 

 old age. With the completion of the cycle in a moist climate the 

 condition of a peneplain is reached, when the region is worn down 

 to essential uniformity, with but little elevation above sea-level. 



* From yXv-wTos, carved, and yhn^is, origin 



82y 



