280 



PHYSICAL GEOLOGY 



Mountains produced by vulcanism. Many of the highest 

 isolated mountains are volcanic cones (p. 46). Fujiyama, 

 a volcanic mountain in Japan (Fig. 294), has an elevation 

 above sea level of 12,365 feet. Many volcanic piles surpass 

 Fujiyama in height, but few, if any, in symmetry of form. 

 Aconcagua, an Andean cone on the border of Chile and 

 Argentina, reaches 22,860 feet. 



Many mountains have been formed also by massive in- 

 trusions of lava which have domed or lifted the overlying 

 strata high above the level of the surrounding country 



FIG. 294. Cone of Fujiyama, Japan. 



(p. 51). Frequently the cover of sedimentary rocks has been 

 removed partially by erosion, exposing the central core of 

 igneous rocks, from which the sedimentary beds often dip 

 more or less uniformly in all directions. The harder sedi- 

 mentary layers, wearing down less rapidly than the softer 

 ones, may stand out as rudely circular ridges alternating 

 with race- track shaped valleys, all of which inclose the 

 igneous center. The Henry Mountains of Utah (p. 50), 

 the Bear Paws and Little Snowies of Montana, and the 

 Elk and Park ranges of Colorado are examples of this general 

 class of mountains. 



