624 



SCIENTIFIC RECREATIONS. 



geography will remember, but which need not be separately treated of. We 

 must, However, refer to plains, plateaus, and lakes. The mountains also play 

 a most important part in Physical Geography and in "Climatology," as they 

 collect the vapours for rain, and make the valleys fertile, and thick with 

 vegetation. We have spoken of the mountains under GEOLOGY, and the 

 various formations and strata will be found enumerated there, but now we 

 have to do with the mountain chains in their physical aspect as regards their 

 shape and appearance on the globe. 



Any elevation rising from a base more than 1,000 feet may fairly be 

 termed a mountain, and solitary mountains are usually volcanic, because 

 eruptive rock does not produce chains of mountains. The origin of 

 mountains is probably due to the contraction and compression of the crust of 

 the earth not merely the surface, but the whole thickness between us and the 



Fig. 711. Earthquake fissures. 



supposed molten interior. Mountains did not exist from everlasting, for the 

 very good reason that they are (in most cases) composed of stratified rocks. 

 Stratified rocks are sedimentary rocks, and must have been deposited below 

 water, and hardened long before they were thrust up by pressure. Moreover, 

 we find (as has already been explained) shells and remains of marine animals 

 on the higher summits, which prove to demonstration that these mountains 

 are composed of rocks which were laid down under the sea. 



Professor Dana was one of the first geologists to advance the theory 

 that contraction and lateral displacement are the causes of the elevation of 

 mountains. A very good illustration of this theory was made by Chamontier, 

 who covered an india-rubber balloon with a thick layer of wax, and when it 

 had hardened sufficiently he pricked a hole in the bladder, which immediately 

 contracted, and the wax at once rose up into tiny similitudes of mountains, 

 showing in a sufficiently clear manner that such protuberances may be 



