208 Adventures in Scenery 



Higher still, however, on the bare rock slope at the immediate 

 base of Sentinel Dome, scattered boulders indicate that at a 

 very early stage in the history of the region the ice may have 

 reached an altitude of 7,900 feet, or fully 700 feet above 

 Glacier Point, and nearly 4,000 feet above the Valley floor. 



It is apparent that ice has played an important part in giving 

 the Yosemite Valley its present form. Other canyons other 

 yosemites were cut in the hard rocks of the great Sierra range, 

 and in these canyons ice has left its mark. All the canyons were 

 first formed by running water, and all were scoured and 

 changed by moving ice. No other of the great canyons that 

 mark the western slope of the Sierra Nevada compare in 

 grandeur of scenery with the Yosemite Valley. Why, it is 

 natural to ask, the outstanding features of the Yosemite Valley? 



Causes of the Great Gorge of the Yosemite 



The key to the understanding of this remarkable gorge lies 

 in the character of the rocks in which the gorge was cut. To 

 understand why the part of the valley of the Merced that is 

 known as the Yosemite Valley is there, in other words the reason 

 why such a valley exists, it is needful to look at the rock for- 

 mations in which and through which the great chasm has been 

 cut. This involves consideration of the character and some- 

 thing of the history of the rocks of the region. 



The Merced River starts from among the high peaks and 

 crags of the High Sierra, and flows in a southwesterly course 

 down the western slope of the Sierra Nevada, and joins the San 

 Joaquin on the bottom of the Great Valley of California. It 

 is what geologists term a "superimposed" river, its course being 

 determined sometime during the hundred million years during 

 which the ancient "roof" that covered the great Sierra batholith 

 was being removed by erosion and weathering. 



It will be recalled from a previous chapter (Chapter XIV) 

 that a vast batholith or lake of molten rock was upwelled from 

 the depths of the earth, uplifting the sedimentary formations 



