Mountain Rains

Caused by movement of winds rising upover mountains; so called by Abercromby 1887. they are inverted, giving a fan-shaped structure. So great a variation must, it would seem, be due to more than one cause, and theories have been many and various. Omitting the more fanciful, we find the others chiefly based on two principles, the secular contraction of the earth, and the changes ensuing on the formation of ma ive sedimentary deposits. That the first may be a real cause it is impo ible to deny. The shrinking of the cooling nucleus from the cold crust must cause a certain amount of crumpling, and out of the ridges thus formed mountains may be carved by erosion. But physicists deny its sufficiency, and maintain that no allowable amount of contraction can account for the mountain ma es of the globe. A modification of this theory calls to its aid a certain additional amount, due to the slowing down of the earth's rotation and the consequent diminution of the centrifugal force. But this is of little avail except near the equator. The second theory is based on the expansion of thick ma es of sediment by the heat that enters them from below, which is estimated by some to be great enough to cause folding of the strata. This theory has lately been worked out fully by T. M. Reade. Like the other, it is open to serious objections, and it is impo ible to admit that either is firmly established. In any case, it must be borne in mind that these theories merely supply the folded strata. Existing mountains have almost all been carved from these by the secondary action of water, and are in most cases but fragments of the original arches, anticlinal and quaquaversal mountains being comparatively rare.