316 ELEMENTARY GEOLOGY 
tain growth, at least not north of Arkansas and Indian 
Territory. | 
There is much irregularity in the direction of moun- 
tain chains, although more of the extensive mountain 
ranges of the world extend north and south than east 
and west. The most remarkable instance of north and 
south extending chains is furnished by the ranges of 
North and South America, which form one nearly con- 
tinuous mountain series from Alaska to Cape Horn. 
On the continents there are usually two or three 
prominent sets of mountains. In North America there 
isan old mountainous highland in Canada, and two sets 
of mountains, the Appalachians and the western Cordil- 
leras, which extend from northern to southern regions. 
These three axes are the skeletons about which the con- 
tinent has been built. By their destruction, sediments 
have been produced and deposited in the neighboring 
seas, and from these accumulations, land masses have 
been made around the mountainous framework. A 
similar condition may be seen in South America and 
Africa, and it is from this that these continents have 
obtained their generally triangular shape; but the 
Australian and Eurasian continents are not so typical. 
Taking as types the two great sets of mountains in 
this country, those of the east and west, we find that 
the mountain masses are really broad plateau uplifts, 
on which the real mountains exist as smaller wrinkles 
