[Note 22:  This has a reference to very curious observations which we made upon the east coast where these mountains terminate, and which I am to describe in the course of this work.]

“Among the masses of limestone lately broken off for use, and having the fractures fresh, I found the forms of cockles quite distinct; and in great abundance.—­I send you three pieces of this kind,” etc.

It may perhaps be alleged that those mountains of Cumberland and Tweedale are not the primary mountains, but composed of the secondary schistus, which is every where known to contain those objects belonging to a former earth.  Naturalists who have not the opportunity of convincing themselves by their proper examination, must judge with regard to that geological fact by the description of others.  Now it is most fortunate for natural history, that it has been in this range of mountains that we have discovered those marks of a marine origin; for, I shall afterwards have occasion to give the clearest light into this subject, from observations made in other parts of those same mountains of schist, by which it will be proved that they are the primary strata; and thus no manner of doubt will then remain in the minds of naturalists, who might otherwise suspect that we were deceiving ourselves, by mistaking the secondary for the primitive schistus.

I have only farther to observe, that those schisti mountains of Wales, of Cumberland, and of the south alpine part of Scotland, where these marine objects have been found, consist, of that species of stone which in some places makes the most admirable slate for covering houses; and, in other parts, it breaks into blocks that so much resemble wood in appearance, that, without narrow inspection, it might pass for petrified wood.

We are therefore to conclude that the marks of organised bodies in those primary mountains are certainly found; at the same time the general observation of naturalists has some foundation, so far as the marks of organised bodies are both rarely to be met with in those masses, and not easily distinguished as such when they are found.

But this scarcity of marine objects is not confined to those primary mountains, as they are called; for among the most horizontal strata, or those of the latest production, there are many in which, it is commonly thought, no marine calcareous objects are to be found; and this is a subject that deserves to be more particularly considered, as the theory may thus receive some illustration.

Sandstone, coal, and their accompanying strata, are thought to be destitute of calcareous marine productions, although many vestiges of plants or vegetable productions are there perceived.  But this general opinion is neither accurate nor true; for though it be true that in the coal and sandstone strata it is most common to find marks of vegetable production, and rarely those calcareous bodies which are so frequent in the