§ 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. 191); 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.