. Elements of geology : a text-book for colleges and for the general reader. Geology. 252 STRUCTURE COMMON TO ALL ROCKS. 3 ^ lateral pressure—this lies still in the field of discussion. We shall dis- cuss it briefly in its proper place. Mountain Structure. A mountain-range, then, may be regarded as a mass of enormously thick strata crushed together laterally and swelled up along the line of crushing. We have said that this mode of origin is revealed in its structure. We can best make this plain by an experiment. Suppose, then, we place, one atop another, several layers of any plastic substance
. Elements of geology : a text-book for colleges and for the general reader. Geology. 252 STRUCTURE COMMON TO ALL ROCKS. 3 ^ lateral pressure—this lies still in the field of discussion. We shall dis- cuss it briefly in its proper place. Mountain Structure. A mountain-range, then, may be regarded as a mass of enormously thick strata crushed together laterally and swelled up along the line of crushing. We have said that this mode of origin is revealed in its structure. We can best make this plain by an experiment. Suppose, then, we place, one atop another, several layers of any plastic substance, such as wax, so as to make together a prismatic mass, as represented in section in Fig. 219, A, and the whole resting on a smooth oiled slab of glass or steel, so that -5 — there shall be no friction or adhesion. Suppose, further, that very gentle heat be applied beneath along the middle line, so as to soften slightly this part. Of course, such soft- ening would be greatest at the bottom, and become less and less upward ; also greatest along the middle line, and become less and less outward. This is rep- resented in the figure by the shading and in nature by the metamor- phic softening, of which we will speak later. Suppose, now, we place a board on each side of the prismatic mass, and press gradually together. All the layers will be thickened and folded, and the whole mass swelled up along the central line into something like Fig. 219, B. We have in miniature both the structure and the mode of formation of a mountain- range. In a similar way, but on a larger scale, all great mountain-ranges seem to have been Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. New York : D. Appleton and Co.
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