often accompanied by displacement of the strata, owing to which the
crust has been vertically elevated on one side or lowered on the other,
and such displacements (or "faults") sometimes amount to thousands of
feet. It is only occasionally, however, that such fractures are
accompanied by the extrusion of molten matter; and in the North of
England and Scotland dykes of igneous rock, such as basalt, which run
across the country for many miles in nearly straight lines, often cut
across the faults, and are only rarely coincident with them.
Nevertheless, it can scarcely be a question that the grand chain of
volcanic mountains which stretches almost continuously along the Andes
of South America, and northwards through Mexico, has been piled up along
the line of a system of fissures in the fundamental rocks parallel to
the coast, though not actually coincident therewith.

(_c._) _The Cordilleras of Quito._--The structure and arrangement of the
Cordilleras of Quito, for example, are eminently suggestive of
arrangement along lines of fissure. As shown by Alexander von
Humboldt,[5] the volcanic mountains are disposed in two parallel chains,
which run side by side for a distance of over 500 miles northwards into
the State of Columbia, and enclose between them the high plains of Quito
and Lacunga. Along the eastern chain are the great cones of El Altar,
rising to an elevation of 16,383 feet above the ocean, and having an
enormous crater apparently dormant or extinct, and covered with snow;
then Cotopaxi (Fig. 2), its sides covered with snow, and sending forth
from its crater several columns of smoke; then Guamani and Cayambe
(19,000 feet), huge truncated cones apparently extinct; these constitute
the eastern chain of volcanic heights. The western chain contains even
loftier mountains. Here we find the gigantic Chimborazo, an extinct
volcano whose summit is white with snow; Carihuairazo[6] and Illiniza, a
lofty pointed peak like the Matterhorn; Corazon, a snow-clad dome,
reaching a height of 15,871 feet; Atacazo and Pichincha, the latter an
extinct volcano reaching an elevation of 15,920 feet; such is the
western chain, remarkable for its straightness, the volcanic cones being
planted in one grand procession from south to north. This rectilinear
arrangement of the western chain, only a little less conspicuous in the
eastern, is very suggestive of a line of fracture in the crust beneath.
And when we contemplate the prodigious quanti