1906.] 



SEE— THE CAUSE OF EARTHQUAKES. 32] 



occurring under neighboring areas. This latter result is impossible, 

 since observations show that the matter under mountains not only 

 is not denser than the average, but actually lighter by an appreciable 

 quantity. We know, therefore, that the wrinkling has not con- 

 densed the matter underlying the mountains. 



On the other hand, it seems equally incredible that the shrink- 

 age of the whole globe should be brought forward to one point, as 

 if the crust were loose from the globe it covers. No part of the 

 theory of mountains formed by wrinkles of the crust is to be seri- 

 ously entertained. Besides the difficulties just mentioned, the 

 postulated radial shrinkage of 12 miles is too great. It may well be 

 doubted whether a shrinkage of one mile in the radius has taken 

 place since the continents began to emerge from the oceans. 



Professor Suess (Vol. II, p. 552) says: 



"As a result of tangential thrusts, the sediment of this (Mediterranean) 

 Sea were folded together and driven upwards as a great mountain range, 

 and the Alps have, therefore, been described as a compressed sea." 



We must, therefore, seek the explanation of the formation of the 

 Alps in some process by which this folding can have taken place in 

 the sea, or along its borders, and thus w^e reach the theory outlined 

 in this paper. 



§ 19. Why zee abandon the contraction theory of mountain for- 

 mation. 



While the considerations here adduced for the origin of moun- 

 tains seem conclusive, it may not be wholly without interest to point 

 out some difficulties which are not satisfactorily met by the con- 

 traction theory, which is the only one now^ in general use. It is 

 usually stated that mountains result from a crumpling of the 

 earth's crust, and that the crumpling takes place along the principal 

 lines of weakness. This theory fails to explain the origin of isolated 

 peaks or associated groups of peaks which sometimes rise like cones 

 or groups of cones, often more or less intersecting, in the midst of 

 comparatively regular plains. \A theory with this serious defect is 

 highly unsatisfactory. 



If then the contraction theory fails to explain isolated peaks and 

 groups, which are sometimes pushed up in comparatively level 

 plains, and fails to explain the conspicuous parallelism to the sea- 



