cliff, traverse the deepest valleys, and scale
the highest mountains, carefully examining their formation, disposition,
and substance, and are thus enabled to obtain some knowledge of the
earth's stomach, as it were, by scrutinising the deposits and eruptive
ejectments on its surface. For example, we come to 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 that 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 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 materials 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 rocks of these two
mountains, and by calculating the thickness right through these strata
could say to what depths the rock of the mountain extended below. In
this way has the interior of the globe been examined, and its contents
and arrangement, for several miles below the surface, ascertained. The
result of such inspection we leave the author of the _Vestiges_ to
describe:--

"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 great inclined masses,
while in many cases there has been projected through the rents
rocky matter more or less resembling the great inferior crystalline
mass. This rocky matter must have been in a state of fusion from
heat at the time of its projection, for it is often found to have
run into and filled up lateral chinks in these rents. There are
even instances where