many instances, be inferred for the depth of many miles by other
means of observation. We see a mountain composed of a particular
substance, with strata, or beds of other rock, lying against its
sloped sides; we, of course, infer that the substance of the mountain
dips away under the strata which we see lying against it. Suppose
that we walk away from the mountain across the turned up edges of the
stratified rocks, and that for many miles we continue to pass over
other stratified rocks, all disposed in the same way, till by and bye
we come to a place where we begin to cross the opposite edges of the
same beds; after which we pass over these rocks all in reverse order
till we come to another extensive mountain composed of similar
material to the first, and shelving away under the strata in the same
way. We should then infer that the stratified rocks occupied a basin
formed by the rock of these two mountains, and by calculating the
thickness right through these strata, could be able to say to what
depth the rock of the mountain extended below. By such means, the
kind of rock existing many miles below the surface can often be
inferred with considerable confidence.

The interior of the globe has now been inspected in this way in many
places, and a tolerably distinct notion of its general arrangements
has consequently been arrived at. It appears that the basis rock of
the earth, as it may be called, is of hard texture, and crystalline
in its constitution. Of this rock, granite may be said to be the
type, though it runs into many varieties. Over this, except in the
comparatively few places where it projects above the general level in
mountains, other rocks are disposed in sheets or strata, with the
appearance of having been deposited originally from water; but these
last rocks have nowhere been allowed to rest in their original
arrangement. Uneasy movements from below have broken them up in