86 



The National Geographic Magazine 



the Forum, and other standard period- 

 icals, are well known ; while his grace- 

 ful and instructive lectures, based on 

 personal observations in India, Kg3'pt, 

 South Africa, Central America, the Phil- 

 ippines, and other remote regions, live 

 in the memory of thousands. 



W J M. 



THE ORIGIN OF YOSEMITE 

 VALLEY.* 



MR. TURNER finds that the higher 

 part of the Sierra Nevada has been 

 glaciated, and in support of this belief in- 

 stances numerous cases of glacial mark- 

 ings and morainal deposits. 



If there is any one feature of the 

 higher parts of the Sierra which stands 

 out in bold relief, so that " he who runs 

 may read," it is the fact that it has been 

 covered by glacial ice in sheets and 

 streams, and that at a very lecent time. 

 There is no need to search for glacial 

 scratches or moraines. The whole as- 

 pect of the terrane is that of great sheets 

 of bare granite, not yet covered with 

 soil, with rounded surfaces, cut by deep 

 U-shaped caiions, containing thousands 

 of lake basins, and presenting cirques 

 and hanging valleys ; in short, ever}^- 

 thing in the field of vision tells the story 

 of a wholesale ice invasion. Nor was it 

 a brief one, but one which lasted for 

 many centuries, during which cubic 

 miles of rock were carried away, cations 

 thousands of feet deep were excavated, 

 and the level of the country planed down 

 to an enormous extent. 



As to the potency of a glacier for the 

 work of erosion, Mr. Turner is among 

 the few remaining upon the negative 

 side. His argument, however, simply 



* The Pleistocene GeoloQV of the South Central 

 Sierm Nevada, ivith Especial Refereiice to the 

 Origin of Yoseinite Vallev. By Henry Ward 

 Turner. Proceedings of the California Acad- 

 emy of Sciences, Vol. i. No. 9. 



consists in a denial of the ability of a 

 glacier to excavate gorges. That the 

 gorges in the high Sierra were cut by 

 glaciers is true nevertheless. They are 

 plainly the result of channel, not valley, 

 erosion, and channel erosion upon such 

 a scale as this is done only by ice. The 

 line of demarcation between channel and 

 valley erosion in the caiions of the Sierra 

 is clearly marked, and can be deter- 

 mined, one might almost say, to a foot — 

 i. e. , the point at which the present visi- 

 ble marks of ice cease and those of water 

 begin. I do not mean that the ice may 

 not have excavated farther down the 

 cations, but that below certain points, 

 easily distinguished, the subsequetit ac- 

 tion of water has masked that of ice. If 

 other proof of the competency of glaciers 

 to do the work of erosion upoti a large 

 scale were wanting, the presence every- 

 where of hanging valleys is in itself evi- 

 dence conclusive. There is no other 

 known agency which could produce 

 them, and today we see them in process 

 of production everywhere in glacial re- 

 gions, tiotably itpon ihe Alaskan coast, 

 where there are thousands of them under 

 construction before our eyes. 



Holding such opiniotis concerning the 

 erosive power of glaciers, it is to be ex- 

 pected that Mr. Turner attributes the 

 creation of the Yosemite Valley to other 

 agencies thait ice ; indeed, he attributes 

 it to aqueous erosion, aided by systems 

 of fractures in the granite. He finds 

 tio significance in the fact that Tenaj^a 

 Cation is vastly greater in breadth and 

 depth, as he states, than could be created 

 b)^ the present Tenaya Creek. He passes 

 over without notice the significant fact 

 that every stream, excepting Tenaya 

 Creek, enters Yosemite Valle}^ through 

 a hanging valley, and that the character 

 of the Merced Valley changes abruptly 

 and suddenly to a V-shaped gorge two 

 or three miles below Fort Monroe, at 

 the foot of Yosemite Valley. 



It is perfectly obvioits to those familiar 

 with glacial phenometia that Yosemite is 



