VI MOUNTAINS 215 
are no mere accidents, but that for every 
mountain chain, for every peak and valley, 
there is a cause and an explanation. 
The origin of Mountains is a question of 
much interest. The building up of Volcanoes 
is even now going on before our eyes. Some 
others, the Dolomites for instance, have been 
regarded by Richthofen and other geologists 
as ancient coral islands. The long lines of 
escarpment which often stretch for miles across 
country, are now ascertained, mainly through 
the researches of Whitaker, to be due to the 
differential action of aerial causes. The gen- 
eral origin of mountain chains, however, was 
at first naturally enough attributed to direct 
upward pressure from below. To attribute 
them in any way to subsidence seems almost 
a paradox, and yet it appears to be now well 
established that the general cause is lateral 
compression, due to contraction of the under-— 
lying mass. The earth, we know, has been 
gradually cooling, and as it contracted in doing 
so, the strata of the crust would necessarily be 
thrown into folds. When an apple dries and 
shrivels in winter, the surface becomes covered 
