STUDIES, SCIENTIFIC AND SOCIAL 



there is a ravine with waterfalls as the upper outlet also, 

 but in almost every case there is some break in the rock 

 walls on one side or the other with easy slopes for the 

 entrance of men and animals. 



The only considerable valleys that can be classed as 

 originally inaccessible — though of course no valley, any 

 more than any mountain, is absolutely so — seem to be, the 

 Yosemite in California, and the vallej^s of the Grose and 

 Cox rivers in New South Wales. It may, therefore, be 

 interesting to describe these valleys, which are in many 

 ways very remarkable. The theories that have been sug- 

 gested to account for them may then be considered ; and 

 we shall thus be led to discuss the general theory of 

 valley-formation and the peculiar combination of condi- 

 tions which in these two very dissimilar cases have led to a 

 somewhat similar result. 



The Yosemite Valley and its su2yposed Origin. 



The Yosemite valley is a portion of the upper course of 

 the Merced River, which rises near the summit of the 

 Sierra Nevada about 170 miles almost due east of San 

 Francisco. This great mountain range, forming the 

 western edge of the lofty table-land of which the Rocky 

 Mountains form the eastern border, has a very gradual 

 upward slope from the central valley of California, the 

 distance from the foothills to the summit varying from 

 sixty to eighty miles, while the height is from 8,000 to 

 nearly 15,000 feet. This average slope of from 100 to 

 250 feet in a mile is rendered exceedingly irregular by 

 numerous large winding valleys, some with easy slopes, 

 some more precipitous, and all more or less covered with 

 forest so as to render the journey from one point to another 

 both circuitous and difficult. The higher portion of the 

 Sierra Nevada is usually of granitic rock, lower down arc 

 metamorphic slates, followed by enormous beds of late ter- 

 tiary gravels, which are often covered with great sheets of 

 lava and ashes, bearing witness to the numerous volcanoes 

 on the summit of the range at a period geologically 

 very recent. The Yosemite valley is situated a little 



