ORIGIN OF MOUNTAIN RANGES. 565 



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 eqtially rigid in 

 every part. But if there be a sub-crust layer of liquid or semi- 

 liquid 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 sup- 

 posed. 



3. But again : it has been objected that the lines of yielding 

 to interior contraction ought not to run in definite directions for 

 lo?ig 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 circum- 

 ferential shortening necessary to produce the foldings of some 

 mountains is simply incredible ; for it would disarrange the sta- 

 bility 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. Now this would make a decrease 

 of diameter of the earth of twenty-eight miles in the one case 

 and twenty-three in the other. This would undoubtedly 

 seriously quicken the rotation and shorten the day. This seems 

 indeed startling at first. But when we remember that the 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 any- 

 thing catastrophic in this readjustment of rotation. Mountains 

 are not formed in a day nor in a thousand years. It requires 



