But I shall suppose Lasius has informed our author that there had been a petrifaction in this case; and, before I admit this example of the formation of granite, I must ask what sort of a granite it was;—­whether of two, three, or four ingredients; and, how these were disposed.  If, again, it were not properly a granite, but a stone formed of granite sand, What is the cementing substance?—­Is it quartz, felt-spar, mica, or schorl?—­or, Was it calcareous?  If our author knows any thing about these necessary questions, Why has he not informed us, as minutely as he has done with regard to the dimensions of the mole, with which we certainly are less concerned?  If, again, he knows no more about the matter than what he has informed us of, he must have strangely imposed upon himself, to suppose that he was giving us an example of the formation of granite in the moist way, when he has only described an effectual way of retaining water, by means of sand and mud.

CHAP.  III.

Of Physical Systems, and Geological Theories, in general.

In the first chapter I have given a general theory of the earth, with such proofs as I thought were sufficient for the information of intelligent men, who might satisfy themselves by examining the facts on which the reasoning in that theory had been founded.

In the second chapter, I have endeavoured to remove the objections which have been made to that theory, by a strenuous patron of the commonly received opinion of mineralogists and geologists,—­an opinion which, if not diametrically opposite, differs essentially from mine.  But now I am to examine nature more particularly, in order to compare those different opinions with the actual state of things, on which every physical theory must be founded.  Therefore, the opinions of other geologists should be clearly stated, that so a fair comparison may be made of theories which are to represent the system of this earth.

Now, if I am to compare that which I have given as a theory of the earth, with the theories given by others under that denomination, I find so little similarity, in the things to be compared, that no other judgment could hence be formed, perhaps, than that they had little or no resemblance.  I see certain treatises named Theories of the Earth; but, I find not any thing that entitles them to be considered as such, unless it be their endeavouring to explain certain appearances which are observed in the earth.  That a proper theory of the earth should explain all those appearances is true; but, it does not hold, conversely, that the explanation of an appearance should constitute a theory of the earth.  So far as the theory of the earth shall be considered as the philosophy or physical knowledge of this world, that is to say, a general view of the means by which the end or purpose is attained, nothing can be properly esteemed such a theory unless it lead, in some degree, to the forming of that general view of things.  But now, let us see what we have to examine in that respect.