The linear regions of elevations of the earth’s surface, as we may term them, in contradistinction to the plateaus which are characterized by breadth rather than by length, have been projected in the form of mountain chains, as has been already hinted, through huge fissures made by the rending of the earth’s crust. The upheaval to fill the seam has, in some cases, been all made at once; in others, in a succession of periods. The uniform agreement of all the geological strata or their diversity decides this point. Sometimes the rocky strata are laid bare and easily investigated. Often, however, the observer is obliged to draw conclusions from a part to the whole. Yet in all cases the mountain, in contradistinction to the adjacent plateau, is the tract which has been thrust through the crust. The frequent steep and lofty precipices show the immensity of the internal force required to lift the mountains from their places, while the lines of stratification indicate the direction of upheaval. The rifting of a seam in the earth’s crust was the first step in the formation of mountains; the filling up of the seam by liquid matter, the second step. The upheaval of Asia, from the Persian plateau to Gobi, in a line 60° N. E., seems to be connected with the most ancient revolution which the earth’s crust ever experienced. The mountains there are, therefore, more modern in origin than the plateau on which they stand. The direction of the chain, in all cases, seems to have been dependent on the direction of the fissure in the earth’s crust, which the mountain range afterward fills. The breaking through the crust necessarily occurred when the pressure beneath the surface was very great, or when a moderate pressure was exerted beneath a thin crust, where the resistance was slight. The latter case seems to have been prevalent in most plateau regions. Their own gradual upheaval probably thinned the surface, and made it more liable to fracture. This accounts for the fact that the greatest mountains of the globe are found contiguous to plateaus. And the broader the original seam in the crust was, the broader the mountain range which rose to fill it, either at a single upheaval, or in a series of convulsive throes projecting successive masses of molten matter from below. In the latter cases the strata thus formed lie on each other like the leaves of a book, their constitution changing according as the more advanced stages of melting in the vast internal caldron throw out more metamorphosed rocks. These later layers rose to a greater or less height on the sides of the partially-formed mountain, according to their specific gravity, their more or less fluid state, and their rapidity of cooling, as we can now see by examining the layers in their present permanent condition.