With regard to the last, the opinions of philosophers have been so dissonant, so vague, and so unreasonable, as to draw to no conclusion.  Some suppose the land to be discovered by the gradual retreat of the ocean, without proposing to explain to us from whence had come the known materials of a former earth, which compose the highest summits of the mountains in the highest continents of the earth.  Others suppose the whole of a former earth to have subsided below the bottom even of the present sea, and together with it all the water of the former sea, from above the summits of the present mountains, which had then been at the bottom of the former sea.  The placing of the bottom of the sea, or any part of it, in the atmosphere so as to be dry land, is no doubt a great operation to be performed, and a difficult task to be explained; but this is only an argument the more for philosophers to agree in adopting the most reasonable means.

But though philosophers differ so widely in that point, this is not the case with regard to the concretion of mineral bodies; here mineralists seem to be almost all of one mind, at the same time without any reason, at least, without any other reason than that false analogy which they have inconsiderately formed from the operations of the surface of this earth.  This great misunderstanding of mineralists has such an extensive and baneful effect in the judging of geological theories, that it will be proper here to explain how that has happened, and to shew the necessity of correcting that erroneous principle before any just opinion can be formed upon the subject.

Fire and water are two great agents in the system of this earth; it is therefore most natural to look for the operation of those agents in the changes which are made on bodies in the mineral regions; and as the consolidated state of those bodies, which had been collected at the bottom of the sea, may have been supposed to be induced either by fusion, or by the concretion from a solution, we are to consider how far natural appearance lead to the conclusion of the one or other of those two different operations.  Here, no doubt, we are to reason analogically from the known power and effects of those great agents; but, we must take care not to reason from a false analogy, by misunderstanding the circumstances of the case, or not attending to the necessary conditions in which those agents act.—­We must not conclude that fire cannot burn in the mineral regions because our fires require the ventilation of the atmosphere; for, besides the actual exigence of mineral fire being a notorious matter of fact, we know that much more powerful means may be employed by nature, for that mineral purpose of exciting heat, than those which we practise.—­We must not conclude that mineral marble is formed in the same manner as we see a similar stony substance produced upon the surface of the earth, unless we should have reason to suppose the analogy to be complete.  But, this is the very error into which mineral philosophers have fallen; and this is the subject which I am now to endeavour to illustrate.