STRUCTURES COMMON TO ALL ROCKS. 243 



rock, granitic or metamorphic, flanked on either side 

 with uptilted and folded strata, as in Figs. 149, 150. It 



FIG. 149. Ideal section, showing granite axis. 



was formerly supposed that the igneous rock in fused con- 

 dition has pushed up and broken through the strata and 

 appeared ahove them. But it is far more probable that 

 stratified rock once covered the whole, as shown by the 

 dotted lines, and that subsequent erosion has exposed the 



FIG. 150. Ideal section of a mountain-range. 



granitic or metamorphic rocks along the crest where the 

 erosion was greatest. Furthermore, when we remember 

 that mountains are composed of immensely thick series 

 of strata, and that very thick strata are sure to be meta- 

 morphic in their lower parts (page 226), and, moreover, 

 that granite is often but the last term of metamorphism 

 of rocks, it becomes probable that even such mountains 

 as those represented in Figs. 149, 150, are really com- 

 posed wholly of horizontally mashed and crumpled strata, 

 only that, on account of the great thickness and strong 

 crumplinirs, these have become completely metamorphic 

 in their lower parts. 



