ORIGIN OF MOUNTAIN RANGES. $47 



ciated with folding and both with mountain ranges. It is not so 

 universal as folding only because all kinds of strata are not 

 equally affected by it ; being well exhibited only in fine shales. 

 It is important to observe that in slaty cleavage the strike of the 

 cleavage planes is the same as that of the strata, and both the 

 same as the trend of the mountain ; and that the dip of the cleav- 

 age planes is nearly or quite vertical. Whole mountains are thus 

 cleavable from top to bottom. 



5. Granite or Metamorphic Axis. — Some mountains are made 

 up wholly of folded strata. This is the case with the Appalachian, 

 the Coast Range, and the Jura. But most great mountains consist 

 of a granitic or metamorphic axis with stratified flanks. This is 

 conspicuously the case with the Sierra, the Alps, and most other 

 great mountains. So general is this, that the typical structure 

 of ranges may be said to be — a granitic axis forming the crest, 

 and stratified rocks, more or less folded, outcropping on the 

 slopes. This very characteristic structure ought to be explained 

 by a true theory of origin. 



6. Asymmetric Form. — Mountains are not usually symmetric, 

 with crest in the middle and slopes equal on the two sides. On 

 the contrary they usually have a long slope on one side and a 

 steeper, often a very abrupt, slope on the other. The crest or 

 axis is not in the middle but nearer to one side. The earth-wave 

 seems ready to break and often does break with a great fault on 

 the steeper side. The Uinta is perhaps the simplest example. 

 This range rises as a single great fold, but steeper on the north 

 side where there is a fracture and fault of 20,000 feet vertical. 

 Of course in this as in all cases the original fault-cliff has 

 crumbled down to a steep slope, or even been destroyed entirely. 

 The Sierra and Wasatch are remarkable examples of asymmetry. 

 The Sierra rises on the west side from the San Joaquin plains 

 near sea level by a gentle slope fifty to sixty miles long, reaches 

 its crest near 15,000 feet high and then plunges down by a slope 

 so steep, that the desert plains on the east, 4,000 to 5,000 feet 

 above sea level is reached in six to ten miles. There is 

 on this side a fault-cliff nearly 11,000 feet high. The Wasatch 



