Sec. 1. In the 20th paragraph of the last chapter, it was noticed that ordinarily the most irregular contortions or fractures of beds of rock were found in the districts of most elevated hills, the contortion or fracture thus appearing to be produced at the moment of elevation. It has also previously been stated that the hardness and crystalline structure of the material increased with the mountainous character of the ground; so that we find as almost invariably correlative, the _hardness_ of the rock, its _distortion_, and its _height_; and, in like manner its _softness_, _regularity_ of _position_, and _lowness_. Thus, the line of beds in an English range of down, composed of soft chalk which crumbles beneath the fingers, will be as low and continuous as in _a_ of Fig. 16 (p. 151); the beds in the Jura mountains, composed of firm limestone, which needs a heavy hammer stroke to break it, will be as high and wavy as at _b_; and the ranges of Alps, composed of slaty crystallines, yielding only to steel wedges or to gunpowder, will be as lofty and as wild in structure as at _c_. Without this beneficent connection of hardness of material with height, mountain ranges either could not have existed, or would not have been habitable. In their present magnificent form, they could not have existed; and whatever their forms, the frequent falls and crumblings away, which are of little consequence in the low crags of Hastings, Dover, or Lyme, would have been fatal to the population of the valleys beneath, when they took place from heights of eight or ten thousand feet. [Illustration: FIG. 19.]