MOUNTAIN ORIGIN. 251 



amples in the Appalachian range. The parallel folds of the Jura range 

 — seen in cross-section in Fig. 223 — are probably the best examples. 



On mountain-ridges there are always prominent points which are 

 called Peaks, whether formed by volcanic ejections like Mount Shasta 

 or Mount Ranier, or by erosion like Mount Dana or Mount Lyell. 



Mountain-systems are separated by great interior Continental basins 

 like the Mississippi-river basin. Ranges are separated by great inte- 

 rior valleys, like Sacramento and San Joaquin Valley, separating the 

 Sierra from the Coast range. Ridges are separated by lo7igitudinal 

 mountain- valleys, while the transverse valleys which trench the flanks 

 of ranges or ridges head in the passes which separate the peaks. 



Such is the simplest idea of mountain form, partially realized in 

 some cases. But, to an observer looking down from a high peak, a 

 mountain-range often seems to be made up of an inextricable tangle of 

 ridges running and peaks standing in every conceivable direction. 



"NTow, a scientific discussion of mountains is really a discussion of 

 ranges or mountain individuals. For, on the one hand, a mountain- 

 system is only a multiplication of such individuals belonging to the 

 same family, and therefore adds no new element to the discussion ; and, 

 on the other, mountain ridges and peaks belong, mainly at least, to the 

 category of mountain sculpture, not of mountain formation, and there- 

 fore are discussed later. 



Greater Inequalities of the Earth- Surface. — The inequalities of the 

 earth-surface, as already explained (page 167), are of two general kinds, 

 the greater and the lesser. The latter belong to sculpture, and will be 

 taken up later. Of the former there are two orders of greatness, viz., 

 those constituting land-masses and oceanic basins, and those consti- 

 tuting mountain-ranges and intervening valleys. We have already dis- 

 cussed the former ; we now take up the latter. 



Mountain Origin. 



Leaving aside for the present all disputed points, it is now univers- 

 ally admitted that mountains are not usually pushed up by a vertical 

 force from beneath, as once supposed, but are formed wholly by lateral 

 pressure. The earth's crust along certain lines is crushed together by 

 lateral or horizontal pressure and rises into a mountain-range along the 

 line of yielding, and to a height proportionate to the amount of mash- 

 ing. But the yielding is not by rising into a hollow arch, nor into such 

 an arch filled beneath with liquid (for in neither case could the arch 

 support itself), but by a mashing together and a thickening and 

 crumpling of the strata and an upswelling of the whole mass along the 

 line of greatest yielding. That this is the immediate or proximate 

 cause of the origin or elevation of mountains is plainly shown by their 

 structure. As to the ultimate cause — i. e., the cause of the enormous 



