When masses of fluid matter are erupted in the mineral regions among strata which are to form our land; and when those elevated strata are, in the course of time, wasted and washed away, the solid mass of those erupted substances, being more durable than the surrounding strata, stand up as eminences in our land.  Now these often, almost always, form the small insulated mountains which are found so frequently breaking out in the lowlands of Scotland.  They appear in various shapes as well as sizes; and they hold their particular form from the joint operation of two different causes; one is the extent and casual shape of the erupted mass; the other is the degradation of that mass, which is wasted by the influences of the atmosphere, though wasted slower than the strata with which it was involved.

When the formation of this erupted mass has been determined by the place in any regular form, which may be distinguished in the shape of a mountain, it gives a certain character which is often not difficult to read.  Thus, our whin-stone, interjected in flat beds between the regular strata, often presents its edge upon, or near the summit of our insolated mountains and eminences.  They are commonly in the form of inclined planes; and, to a person a little conversant in this subject, they are extremely distinguishable in the external form of the hill.

We have a good example of this in the little mountain of Arthur’s Seat, by this town of Edinburgh.  This is a peaked hill of an irregular erupted mass; but on the south and north sides of this central mass, the basaltic matters had been forced also in those inclined beds among the regular strata.  On the north side we find remarkable masses of whin-stone in that regular form among the strata, and lying parallel with them.  The most conspicuous of these basaltic beds forms the summit of the hill which is called Salisbury Craig.  Here the bed of whin-stone, more than 60 or 80 feet thick, rises to the west at an angle of about 40 degrees; it forms the precipicious summit which looks to the west; and this is an appearance which is distinguishable upon a hundred other occasions in the hills and mountains of this country.

Rivers make sections of mountains through which they pass.  Therefore, nothing is more interesting for bringing to our knowledge the former state of things upon the surface of this earth, than the examination of those valleys which the rivers have formed by wearing down the solid parts of alpine countries.  We have already seen that the wide extensive valley of the Rhone, between Loiche and Kolebesche, as well as the whole extensive circus of the Rosa mountains, has on each side mountains of the same substances, the strata of which are horizontal; consequently, here the valley must have been hollowed out of the solid rock; for there is no natural operation by which those opposite mountains of horizontal strata could have been formed, except in the continuation of those beds.  We are therefore to conclude, that the solid strata between those ridges of lofty mountains had been continuous.