

ORIGIN OF MOUNTAINS. 



799 





Figs. 



1151, 1152. 

 1151. 



very gradually applied. By " very gradually " should be understood 

 movement by the yard or so a century, or that degree of extreme slow- 

 ness which has so often been exemplified in geological history, and 

 which is the most common of nature's methods of progress. The rock, 

 or other solid, though apparently inflexible, will undergo, under such 

 conditions, a molecular movement, adapting it to its new condition. 



In support of this statement, there are the facts respecting ice, stated 

 on page 695. The bending of great masses by their own weight goes 

 on without any fractures of the stretching side ; a movement in the 

 molecules takes place, in which the concave side loses and the convex 

 side gains, so that the density remains throughout the same. There 

 is no reason to doubt that if ice covered a lake to a thickness of a score 

 or more feet, and a slowly-accumulating pressure to a sufficient amount 

 could be brought to bear against one side of it, the ice might be pli- 

 cated over its surface, as boldly and numerously as the formations of 

 the Appalachians. 



This subject is further illustrated by the " flowing of cold metals " 

 when under pressure, first recognized as a principle by Tresca. The 

 pressure, he says, is transmitted 

 from particle to particle through 

 the interior of the mass, and thus 

 tends to produce a flow of metal 

 in the direction of least resist- 

 ance. In well-conducted experi- 

 ments at the Stevens Institute, 

 Hoboken, by Mr. David Towns- 

 end (published in the Journal of 

 the Franklin Institute for March, 

 1878), rectangular blocks of iron, 

 accurately planed and measured 

 (being made about 1*75 inches 

 wide and thick, and 2*5 inches 

 long), were punched cold through 

 the centre with a punch 7-16ths 

 of an inch in diameter. The core 

 which came out (Fig. 1152), was 

 only ll-16ths of an inch (instead 

 of 1-75 inches = 28-1 6ths) long ; 

 and yet, like the punched block, 

 it was essentially unchanged in 

 density. Mr. Townsend's ex- 

 periments and measurements show that over two thirds of the metal 

 which had filled the hole had moved off laterally or in the direction 



^™ t 



1152. 



Fig. 1151. Punch at a depth of 1 J inches. 

 Fig. 1152. Core out. 



