170 Adventures in Scenery 



forced from below toward the surface and sometimes was 

 poured out upon the surface in the form of molten liquid lava. 

 The nature of the interior of the earth is but little known. The 

 causes of the uplifting of the Sierra block and of the down- 

 faulting of the valley blocks adjoining it on the east indeed 

 the causes of the upwarpings and faulting movements that have 

 affected the whole of the Great Basin are not fully under- 

 stood. A block such as that of the Sierra Nevada must have 

 a tremendous depth, and the main fractures that bound it must 

 reach far down into the earth. That the forces involved were 

 deep-seated and of great power is apparent. 



The Main Mass of the Sierra Range 

 a Great Batholith 



Of what manner of rock materials is this huge earth block 

 constituting the Sierra Nevada range built up? It is essentially 

 a block of granitic rocks (Fig. 54) . The block was once cov- 

 ered with sedimentary rocks, which have been mostly removed 

 by erosion. Only on the lower part of its western slope and in 

 some places on its crest are there considerable bodies of other 

 rocks, such as slate, quartzite, limestone, and lava. 



The main mass of the Sierra Nevada range is a vast body of 

 granitic rocks known as a batholith, a term which means "deep 

 rock." A batholith is formed by the welling up from the 

 depths of the earth of highly heated molten rock toward the 

 surface but stopping before reaching it. It thus forms a reser- 

 voir of molten liquid rocks below the surface that has over it 

 a roof of rock formations under which the molten mass is forced 

 from below, but which remained as a cover or roof over the 

 molten rock. 



The granite rocks have been forced up from the depths of 

 the earth in a molten state and have crystallized as they cooled. 

 In the Sierra block occur many different kinds of rocks, as 

 granites, monzonites, granodiorites, diorites, and gabbros. (See 

 Glossary.) For the general reader the granitic rocks may all 



