116 E. C, ANDREWS. 



EROSION AND ITS SIGNIFICANCE. 

 By E. O. Andrews, b.a., Department of Mines, Sydney. 



[Read before the Royal Society of N. S. Wales, August 2, 1911J] 



Introductory. 

 The present note is an attempt to coordinate our know- 

 ledge of stream processes, and to assign them their proper 

 place in the sculpturing of land forms. It is rapidly coming 

 to be seen that in order to explain the origin of certain 

 common but important "facts of form" one must grasp the 

 real significance of the operation of certain highly variable 

 factors, not only when acting individually but also when 

 acting in combination. 



To take a single illustration, it is well known that 

 wherever there are high plateaus in the temperate and 

 tropical regions there one finds great fault scarps, deep 

 narrow senkungsf elder, l and great numbers of minor fault 

 scarps, arranged apparently in the most capricious fashion. 

 On the other hand similar plateau blocks occur in the 

 mountains of Western America, in Alaska, in southern New 

 Zealand, in the Swiss Alps, in Norway and in the Antarctic, 

 and it is almost certain from a consideration of mechanical 

 principles, that in these regions also deep senkungsfelder 

 were formed, nevertheless the intense glaciation to which 

 they have been subjected in more recent times has so 

 modified the preglacial profiles as to obscure them and to 

 make it almost impossible to directly prove their origin 

 by faulting, by stream action, or by a combination of 

 these two activities. It is a remarkable fact, however, 

 that so soon as one leaves the region of intense glaciation 

 in such areas, one has the evidence of strong recent fault- 



1 A senkungsfeld is a sunken, or dropped, block of the earth's crust. 





