PHYSICAL GEOGRAPHY. 
55 
land is about 3405 feet above the sea. On the 
continent of Europe, the most elevated mountain is 
Mont Blanc, which forms the highest peak of the 
Alps, and rises 15,660 feet above the sea. The Py- 
renees are about 11,000 feet high, and Etna is 
equally lofty. 
In Africa, the highest mountains are those of 
Abyssinia, which are about 15,000 feet high. On 
our own continent, the highest points are those of 
the Andes ; Chimborazo being elevated 21,425 feet, 
while several other peaks are equally lofty. The 
volcano of Popocatepetl, in Mexico, is 17,720 feet 
high ; the Rocky Mountains* are stated to be proba- 
bly still higher. 
The external structure and configuration of hills 
and mountains forms a curious and interesting, al- 
though hitherto neglected branch of geological inqui- 
ry. These elevations have been shown to perform 
^an important function in the economy of nature, 
^by collecting and duly distributing over the earth's 
-surface the waters derived from the atmosphere; 
and, to fit them for this office, a suitable struc- 
ture has been given ; a structure which is infinitely 
varied, according to the nature and composition of 
the mass. The more perfect representation of the 
undulations of the surface in modern maps, and, 
more especially, in those constructed for military 
purposes, will, however, in time, throw much light 
upon this subject, and more firmly establish those 
principles of which, at present, we have only a 
vague and general idea. As regards the direction 
of elevated ranges of ground, there is generally one 
or more extending through every continent and isl- 
and, and thus determining its general form and con- 
figuration. The mountains of Great Britain present 
<in example of thi« kind, and a still more striking one 
is afforded by the vast chain of mountains which 
* 18,000 feet, according to Prof. Renwick. 
