Itt 
MOUNTAINS AND THEIR ORIGIN. 
the earth’s surface, raised uniformly and in one 
direction. It is the same pressure from below, 
which, when acting with more intense force in 
one direction, makes a narrow and more abrupt 
fold, forming a mountain-ridge, but, when acting 
over a wider surface with equal force, produces 
an extensive uniform elevation. If the pressure 
be strong enough, it will cause cracks and dislo- 
cations at the edges of such a gigantic fold, and 
then we have table-lands between two mountain- 
chains, like the Gobi in Asia between the Altai 
Mountains and the Himalayas, or the table-land 
enclosed between the Rocky Mountains and the 
coast-range of the Pacific shore. 
We do not think of table-lands as mountainous 
elevations, because their broad, flat surfaces re- 
mind us of the level tracts of the earth ; but 
some of the table-lands are nevertheless higher 
than many mountain-chains, as, for instance, the 
Gobi, which is higher than the Alleghanies, or 
the Jura, or the Scandinavian Alps. One of 
Humboldt’s masterly generalizations was his esti- 
mate of the average thickness of the different 
continents, supposing their heights to be levelled 
and their depressions filled up, and he found that 
upon such an estimate Asia would be much 
higher than America, notwithstanding the great 
mountain-chains of the latter. The extensive 
table-land of Asia, with the mountains adjoining 
