302 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



from the end of a glacier is filled with sediment and would 

 cut even very hard rock in a comparatively rapid manner. 

 Moreover, the erosion by water of a glaciated canyon would 

 begin as soon as the ice began to retreat. Thus between 

 the beginning of the ice retreat and the present time there 

 would be a considerable period for erosion, and the V- 

 shaped river canyon would gradually eat its way up stream, 

 obliterating the glacial U-form. 



Lindgren^ describes moraines, in position similar to those 

 of the most western moraines of the Stanislaus and Merced, 

 on the ridges enclosing the valley of the Rubicon River, 

 where it cuts across the northwest corner of the Pyramid 

 Peak quadrangle. Lindgren writes: — 



These facts admit of scarcely any other explanation than that the whole 

 basin of the Rubicon River in this vicinity was at one time filled with ice. If it 

 was, the tongue of the glacier in the canyon must have projected into the adjoin- 

 ing Placerville quadrangle, approaching a least elevation of about 3,000 feet. 

 This seems, however, difficult to believe, for the canyon of the Rubicon 

 basin does not in the Pyramid Peak quadrangle present such decided evi- 

 dence of glaciation as would be expected if the whole deep valley had been 

 filled with ice. 



Mr. Lindgren did not think that the facts in this region 

 warranted the assumption of more than one glacial period ; 

 but the explanation adopted for the glacial phenomena of 

 the Merced and other canyons would appear to apply 

 equally well here. 



8. Evidence of Glaciation in Toscniite Valley. 



Professor J. D. Whitney is perhaps the only geologist of 

 note who doubted the former presence of glacial ice in 

 Yosemite Valley. It may be well, hov/ever, to state specif- 

 ically the proofs of the occupation of the valley by ice. 



Undoubted moraines were found on the valley floor at 

 six points. The one farther east is a medial moraine lying 

 between Tenaya Creek and the Merced near their junction; 

 the others form a group near the western end of the valley. 



1 Pyramid Peak Folio, Geol. Atlas of the U. S. 



