THE MOUNTAIN FRAMEWORK. 117 



heaped up on this ice field in various parts. Then, if a hole 

 be pierced through, the water will rise with increased likeli- 

 hood to overflow. Now these piles of ice exert an effect similar 

 to that of upraised wrinkles in the crust. So it appears that 

 volcanoes may be an incident of the earth's contraction, aa 

 before stated, and that mountain-making may be another in- 

 cident of the same. But there is more to be said. In man} 

 places must occur some crushing together. In the 'mountain 

 folds where the internal constitution and firmness have been 

 strained by flexures, there must be weakness ; and there must 

 occur some of that mashing togetiier which develops heat, inde- 

 pendently of any supply from the molten interior. It is quite 

 intelligible, therefore, that a mountain wrinkle or fold is a 

 zone where heat must be generated, even if lava is not pro- 

 duced, and does not escape from within. Along a mountain 

 fold, in other words, is a zone where the rocks must be sub- 

 jected to that baking or semifusiou in connection with water, 

 which produces the changes called metamorphism. 



It would not be proper to leave the subject in this state, 

 though you have already the gist of the theory of mountain 

 making. If you observe shrewdly, you will discover two 

 features in our mountains on which no light has been thrown. 

 You may experience some difficulty in understanding the ex- 

 planations. But let us try. You know well that all our great 

 mountains exist as long ranges mostly as groups of ranges, 

 and that the prevailing direction of mountain trends is approx- 

 imately north and south. Now, when we consider the wrinkles 

 on the skin of a withered apple, we find them short, and hav- 

 ing also, no uniformity of trend. The analogy is imperfect. 

 There must have-been some other cause than uniform shrinkage 

 to develop the actual mountain folds. 



Let us glance back over the early history of the earth. 

 They tell us it once revolved much more rapidly on its axis 

 than at present. It is not difficult to understand why its rota- 

 tion has been retarded, but we will pass that by. If the rotation 

 has slackened, then the equatorial protuberance has diminished. 

 That is, the equatorial circumference has been shortened more 



