VIEWS OF AMERICAN WRITERS. 885 



Philippson follows Richthofen in treating plains of denudation — 

 "abrasionsflachen " — as the result of wave action.-^ 



The American School. 



Few American writers accept the belief of the English school. The first 

 clear recognition of the importance of subaerial baseleveling should, I 

 believe, be credited to our geologists in the western surveys.f 



Powell's " Exploration of the Colorado river " (1875) brought the 

 American view of the capabilities of subaerial erosion more prominently 

 forward, yet the text does not furnish brief explicit statement directly to 

 the effect that lowlands of denudation may be produced by subaerial 

 agencies. Extracts would lose their flavor apart from their context, but 

 in figuring a section of the wall in the Grand canyon the beveled sur- 

 face of the tilted older strata on which the horizontal Carboniferous strata 

 lie is drawn smooth and even. The overlying beds "are records of the 

 invasion of the sea; the line of separation the record of a long time 

 when the region was dry land " (page 212). Here the imphcation is 

 that the sea gained entrance by depression of the baseleveled land. The 

 overlying strata are regarded as the ruins of some unrepresented land, 

 not of the locally buried land. The explanation is precisely opposite 

 to that given to similar structures by Eichthofen. 



In Poweirs " Geology of the Uinta mountains " (1876) there is a similar 

 absence of explicit account of baseleveled |)lains, apparently because 

 it was not necessary to expand truisms so simple ; but the chapter on 

 degradation very clearly implies the cajmcity of subaerial forces to wear 

 down mountains, however high ; indeed, its burden is to show that the 

 destruction of a lofty range is so much accelerated by steep declivity that 

 its life cannot be much longer than that of a low range. Mountains are 

 " ephemeral topographic forms ; " all existing mountains are geologically 

 recent (page 197). All this without once calling on the aid of sea waves. 



Button's monograph on the "' Tertiary History of the Grand Can3^on 

 district" (1882) is most characteristically American in treatment as in 

 theme. Referring to the sreat unconformity near the base of the canyon 

 walls in the Kaibab and Sheavwits plateaus, he says, on page 207, that — 



"The horizontal Carboniferous beds appear to have been laid down upon the 

 surface of a country which had been enormously eroded and afterward submerged." 



*Stndien iiber Wasserseheiden, 1886, p. 100. 



f Marvine briefly presented the essenoe of the idea in 1873, but he made mention of marine 

 action in a late stage of the process, somewhat after the fashion of the English school. Describ- 

 ing the east slope of the Rocky mountain front range, he wrote : " The ancient erosion gradually 

 wore down the mass of Archean rocks to the surface of the sea, . . . the mnsswas finally 

 leveled off irrespective of structure or relative hardnesses of its beds, by the encroaching ocean, 

 which worked over its ruins and laid them down upon the smoothed surface in the form of the 

 Triassic and other beds " (Hayden's Survey, Rept. for 1873, p. 144). 



XLV-Bui-L. Geoi,. See. Am., Vol. 7, 1895. 



