Page:The Journal of geology (IA journalofgeology11893univers).pdf/139
ing according to him would be evenly distributed everywhere and therefore imperceptible anywhere. This is probably true, and therefore a valid objection in the case of an earth equally rigid in every part. But if there be a sub-crust layer of liquid or semiliquid or viscous, or even more movable or more unstable matter, either universal or over large areas, as there are many reasons to think, then the objection falls to the ground. For in that case there would be no reason why the effects of general contraction should not be concentrated on weakest lines as we have supposed.
3. But again: it has been objected that the lines of yielding to interior contraction ought not to run in definite directions for long distances, but irregularly in all directions. I believe we may find the answer to this objection in the principle of flow of solids under very slow heavy pressure. The flow of the solid earth, under pressure in many directions, might well be conceived as being deflected to the direction of least resistance, i. e., of easiest yielding.
4 But again: it will be objected that the amount of circumferential shortening necessary to produce the foldings of some mountains is simply incredible; for it would disarrange the stability of the rotation of the earth itself. According to Claypole, in the formation of the Appalachian range, the circumference of the earth was shortened eighty-eight miles and in the formation of the Alps seventy-two miles. This would undoubtedly seriously quicken the rotation and shorten the day. This seems indeed startling at first. But when we remember that tidal drag is all the time retarding the rotation and lengthening the day and much more at one time than now, we should not shrink from acceptance of a counteracting cause hastening the rotation and shortening the day, and thus giving stability instead of destroying it. We must not imagine that there would be anything catastrophic in this readjustment of rotation. Mountains are not formed in a day nor in a thousand years. It requires