282 



PHYSICAL GEOLOGY 



FIG. 296. Summits of Endieott Mountains, Alaska. Shows dissected 

 plateau feature. (Brooks, U.S. Geol. Surv.) 



which the upraised beds were much wasted by erosion (Fig. 

 297). 



The destruction of mountains. Unless renewed by dias- 

 trophism or vulcanism, all mountains are in time destroyed 

 by erosion. It is to be noted, too, that the erosion of moun- 

 tains commences as soon as they begin to rise, and continues 

 throughout the long period of their groAvth, as well as after- 

 wards. Accordingly, no mountain due to vulcanism or 



FIG. 297. Diagram showing structure of the beds in the region of the 

 Santa Lucia Range, Cal. (From San Luis, Cal., Geologic Folio, U.S. 

 Geol. Sum.) 



diastrophism ever had the full height which those processes 

 would have given it, if unopposed by erosion. As already 

 pointed out, many mountains have been several times nearly 

 or wholly reduced and revived again. The length of the 

 life of a mountain which has ceased to grow is determined 

 largely by its height, by the resistance of its rocks, and by the 

 character of the climate. Where mountain slopes are steep, 

 as is likely to be the case, erosion is rapid, and the products 



