38 MOUNTAIN AND MOORLAND 



schists and granites may be almost made over again. 

 In short, to use the technical word, mountain-folding 

 is associated with the metamorphosis of rocks. 



There are other mountains known as Dislocation or 

 Block mountains, which are due to the fracturing of 

 the earth's crust and to unequal vertical subsidence. 

 They are blocks of the crust which have maintained 

 their relative position while adjacent tracts have 

 broken away and subsided. Or a great piece of the 

 earth's crust may be tilted up at one side and depressed 

 at the other. We sometimes get a hint of the forma- 

 tion of Block mountains when we watch the breaking 

 up of the ice on a thickly frozen reach of a river where 

 the flow is very slight. Big masses sink down and 

 others are tilted up into prominent blocks. 



The greatest Dislocation mountains in the world are 

 the long parallel ranges of the Great Basin of North 

 America, a remarkable plateau stretching from west 

 to east for some 500 miles between the Sierra Nevada 

 and the Wahsatch Mountains, and extending for 

 nearly 800 miles from north to south. On a much 

 smaller scale are the mountains of Moab and Pales- 

 tine, rising above the great down-sinking of the Jordan 

 Valley and the Dead Sea. The Vosges and the Black 

 Forest represent Dislocation mountains with the 

 broad down-sinking of the Rhine Valley between them. 



Another type of mountain may be included here, the 

 elevation that is produced when the crust is bulged 

 upwards owing to the pressure of a mass of molten 

 rock beneath which had not force enough to form a 

 volcano. It may be roughly compared to a swelling 

 on pie-crust The molten roll that bulges up the crust 

 may intrude into the surrounding strata in the form 



