face of this earth in which the effect
of both those causes must not more or less appear.

But though the effects of those two causes be evident in the
conformation of every mountainous region, it is not always easy to
analyse those effects so as to see the efficient cause. Without sections
of mountains their internal structure cannot be perceived, if the
surface which we see be covered with soil as is generally the case. It
is true, indeed, that the solid bodies often partially appear through
that covering of soil, and so far discover to us what is to be found
within; but as those solid parts are often in disorder, we cannot, from
a small portion, always judge of the generality. Besides, the solid
parts of mountains is often a compound thing, composed both of
stratified and injected bodies; it is therefore most precarious, from
a portion which is seen, to form a judgment of a whole mass which is
unexplored. Nevertheless, knowing the principles observed by nature
both in the construction and degradation of mountains, and cautiously
inferring nothing farther than the data will admit of, some conclusion
may be formed, in reasoning from what is known to what is still unknown.

It is with this view that we are now to consider the general forms of
mountains, such as they appear to us at a certain distance, when we have
not the opportunity of examining them in a more perfect manner. For,
though we may not thus learn always to understand that which is thus
examined, we shall learn, what is still more interesting, viz. that
those mountains have been formed in the natural operations of the earth,
and according to physical rules that may be investigated.

We are to distinguish mountains as being either on the one hand soft and
smooth, or on the other hand as hard and rocky. If we can understand
those two great divisions by themselves, we shall find it easy to
explain the more complex cases, where these two general appearances
partially prevail. Let us therefore examine this general division which
we have made with regard to the external character of mountains.

The soft and smooth mountains are generally formed of the schisti, when
there is any considerable extent of such alpine or mountainous
region. The substance is sufficiently durable to form a mountain, or
sufficiently strong, in its natural state, to resist the greatest
torrent of water; at the same time this fissible substance generally
decays so completely, when expose