is this, that the regularity in the shape of those mountains
arises from the rock of the mountain being either on the one hand an
uniform solid mass, or on the other hand a stratified mass, or one
formed upon some regular principle distinguishable in the shape. In the
first of these, we have a conical or pyramidal shape, arising from the
gradual decay of the rock exposed to the destructive causes of the
surface, as already explained in this chapter. In the second, again, we
find the original structure of the mass influencing the present shape in
conjunction with the destructive causes, by which a certain regularity
may be observed. Now, this original shape is no other than that of beds
or strata of solid resisting rock, which may be regularly disposed in a
mountain, either horizontally, vertically, or in an inclined position;
and those solid beds may then affect the shape of the mountain in some
regular or distinguishable manner, besides the other parts of its shape
which it acquires upon the principle of decay.

In distinguishing, at a distance, those regular causes in the form
of mountains, we may not be able to tell, with certainty, what the
substance is of which the mountain is composed; yet, with regard to the
internal structure of that part of the earth, a person of knowledge and
experience in the subject may form a judgment in which, for coming
at truth, there is more than accident; there is even often more than
probable conjecture. Thus, a horizontal bed of rock forms a table
mountain, or such as M. Bouguer found in the valley of the Madelena. An
inclined rock of this kind forms a mountain sloping on the one side, and
having a precipice upon the upper part of the other side, with a slope
of fallen earth at the bottom; such as the ridges observed by M. de
Saussure from the top of the Cramont, having precipices upon one side,
which also had a respect to certain central points, an observation
which draws to more than the simple structure of the mountain. Were it
vertical, again, it would form a rocky ridge extended in length, and
having its sides equally sloped, so far as the other circumstances of
the place would permit.

Therefore, whether we suppose the mountains formed of a rock in mass, or
in that of regular beds, this must have an influence in the form of this
decaying surface of the earth, and may be distinguished in the shape of
mountains. It is but rarely that we find mountains formed altogether of
rock,