214 



NATURE FOR ITS OWN SAKE 



ridge is a bulge or break in the dome of ma- 

 sonry, and not a string-course where an extra 

 layer of rock is placed for ornament or strength. 

 It seems to be the present scientific conclu- 

 sion that mountains are not formed so much by 

 volcanic action as by the folds or laps in the 

 crust made by the contraction of the earth as it 

 grows older and colder. The illustration used 

 is that of the skin or surface of an apple. It 

 wrinkles in folds as the apple withers and de- 

 creases in size ; and these folds in the skin of 

 the apple correspond to the mountains and val- 

 leys of our earth. The illustration and the 

 conclusion are both very plausible. The long 

 line of the Rockies once lay, perhaps, thousands 

 of feet beneath the flat bed of an inland sea, but 

 some contraction of the earth, some great sink- 

 ing-in of the crust on either side, caused a cor- 

 responding fold to rise, and the result was the 

 long range of mountains from Alaska to Pata- 

 gonia. The high point of the fold came just 

 on the central line of the ridge, and from that 

 outward, on either side, this fold was less 

 marked, producing near at hand the smaller 

 spurs, then the slightly heaved foot-hills, 

 finally merging into the undisturbed plains. 

 The Alps were doubtless formed in a similar 



