MOUNTAINS AND THEIR ORIGIN. 103 
mountains, between the Jurassic and Cretaceous 
periods, the character of the upheaval is the 
same, though there are more cracks at right 
angles with the general trend of the chain, and 
here and there the masses below have broken 
through. But the chain, as a whole, consists of 
a succession of parallel folds, forming long domes 
or arches, divided by longitudinal valleys. The 
valleys represent the subsidences of the crust ; 
the domes are the corresponding protrusions re- 
sulting from these subsidences. The lines of 
gentle undulation in this chain, so striking in 
contrast to the rugged and abrupt character of 
the Alps immediately opposite, are the result of 
this mode of formation. 
After the crust of the earth had grown so 
thick, as it was, for instance, in the later Tertiary 
periods, when the Alps were uplifted, such an 
eruption could take place only through the 
agency of an immense force, and the extent of 
the fracture would be in proportion to the resist- 
ance opposed. It is hardly to be doubted, from 
the geological evidence already collected, that 
the whole mountain-range from Western Europe 
through the continent of Asia, including the 
Alps, the Caucasus, and the Himalayas, was 
raised at the same time. A convulsion that thus 
made a gigantic rent across two continents, giv- 
ing 3gress to three such mountain-ranges, must 
