increase of heat. Such phenomena, many analogous to which are supplied by chymistry, always indicate that one of the two substances, the effects of which are compared, contains the other which causes it, in this union, to enjoy some distinctive property; but which, nevertheless, is susceptible, in certain circumstances, of decomposition, thereby leaving the other substance at liberty to exercise its own peculiar property. Some naturalists, and among others, M.M. SENÉBIER and PICTET, proceeding from these analogies, had already remarked, that the conformity between the effects of light and fire, in certain determinate circumstances, though the effects peculiar to those two fluids are so very different, in their most common phenomena, could arise only from one of the following two causes; either that light contained fire, which in certain circumstances disengaged itself; or that fire contained light, which in certain cases produced it, and from which it disengaged itself in others. This is not the place to discuss that question. I have done so in my Idées sur la Météorologie, and in some Letters addressed to M. de la Métherie, published in his Journal de Physique, where I have assigned my reasons for adopting the last of the propositions of this dilemma, to which the whole of terrestrial physics leads us. Here then we have a proposition, respecting which no further doubt can be entertained: namely, that fire cannot exist without light. Finally, embracing all the modifications of known expansive fluids, and all the luminous phenomena of mineral, vegetable, and animal substances, we cannot avoid perceiving, that the office of rendering objects visible, important as it certainly is to us, is yet the least so

of all those which light performs among the physical operations, to which the organized beings of our globe owe their preservation; that either alone, or by its combination which produces fire, it must have entered into the composition of most known substances on our globe, and in our atmosphere, and that without it nothing of what we observe on our globe would have taken place.

41. Here then I am content to stop in my enquiries into this chain of causes, whence all the known phenomena of our globe have proceeded, because I perceive nothing in physical science that can conduct us beyond that limit. The link immediately more remote ought be the source of that light, which, by its combination with the other elements, points out to us, with such precision, a certain original epoch in the history of the earth, and physical enquiries do not appear to me capable of ever furnishing the least probable conjecture on this head. But this natural boundary, at which I feel compelled to stop, occasions neither obscurity nor confusion in the subsequent phenomena; all of which, setting out thence, proceed regularly from known physical causes; and it is even from their connection with that first link discoverable by physics which I have been tracing, that I conclude at length" That nothing of all that we see on the globe, could begin to be operated, without the union of a certain quantity of light to all the other elements of which it was at first composed; elements which, without it, would have exercised no chymical action on each other; and that accordingly all the known geological phenomena date their origin from the time of this union."

I have now, Sir, completed the first part of the task I imposed on myself, that of pursuing on paper the same analytical method I had observed in our conversations, in order to serve as an introduction to an abridgment of the Geological Letters which I have addressed to M. de la Métherie, in his Journal de Physique; though directing my course in a manner more precise and conformable to the object of these Letters, namely, that of demonstrating the agreement of nature with faith in the earliest of the divine revelations. In pursuance of this plan, I have hitherto given an exposition of the true characters of geological phenomena, and the means which physical science supplies for ascending by them to an epoch in the earliest periods of the earth, when nothing of all that we observe there had as yet been produced. From that epoch therefore I shall set out in the following Letters, in order to trace from thence the principal events which have taken place on our globe; and I shall do so from monuments more intelligible than are the greater part of those of the ancient empires on the continents which we inhabit.

I have the honour to be, &c.

LETTER III.

On the History of the Earth, from the origin of what is now observed upon it, down to the production of the strata of Sand-stone.

SIR,

Windsor, September 18, 1793.

I CONCLUDED my last Letter with this proposition, deduced from the principal geological phenomena, "that nothing of all that we see on our globe could have been operated, had not light been added to, and introduced among the other elements of which its mass consisted; but that as soon as this happened, the chymical operations, which have produced the whole of the phenomena of geology, necessarily began." Thus then it is that nature herself already bears testimony to that great command of the Almighty, at the commencement of the Mosaic narrative :-" Let there be light1!”

1 The following passage, (here quoted by the author in a note, of which the substance will be given) is extracted from the "Mémoire sur les Roches," &c. in the "Journal de Physique," by M. de Do

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1. The operations that took place subsequently to this great epoch, until the creation of man, recited in the first chapter of Genesis, are there divided into six periods, called, in our translations, "days;" and upon the common interpretation of this word it is, that unbelievers have founded their most specious objections against Revelation. For with a slight knowledge of geology, it was easy to oppose many phenomena to a succession of such events as would have taken up only six of our days of twenty-four hours. But it is evident, from the text itself, that this interpretation is erroneous ;-for, first, our days of twenty-four hours are measured by the revolutions of the earth on its

lomieu, whom he considered as the naturalist the most deeply versed in terrestrial physics, and whose views on the general principles of chymistry, and on important points in geology were conformable to his own :- "With M. de Luc, therefore, I shall say, that there was an epoch at which an essential change must have happened in our globe, since from such a change has proceeded all that we observe, which had not been produced before." In regard to an objection which M. Dolomieu afterwards makes, viz. that the simple liquidity of water would be insufficient to account for the commencement of the operations, unless that substance should acquire a principle of activity which does not essentially belong to it, our author states his belief that M. Dolomieu will find in these Letters sufficient reasons for believing that liquidity having once been produced in the mass of elements constituting the globe, by the sole introduction of light, as a new chymical ingredient, nothing was wanting for the commencement of the operation; undertaking to show, in a future work, that at the period when water acquired liquidity, it also acquired a principle of activity, by combining with other elements.

De Luc, however, did not consider water, even after it has acquired a principle of activity, as the only dissolving agent; he maintained that all the elements were reciprocally solvents one of another. ED.