LETTER I.

On the phenomena characterizing the causes that have formerly operated upon the Terrestrial Globe; and particularly on those which fix the date of the origin of our Continents.

SIR,

Windsor, September 1, 1792.

I HAVE not forgotten, that when I had the pleasure of seeing you here, I engaged to furnish you in writing with the substance of our conversations on Geology; the performance of which promise want of time alone had caused me to defer.

You had read in the "Journal de Physique," the Letters I have addressed to the editor, M. DE LA METHERIE, on this subject, so closely connected with your studies and as we soon found that we agreed on many points, it was very easy for us to embrace at once a variety of general views; by which means the different parts of my theory being brought more closely together, you more readily understood the connections and proofs. It then occurred to you that I ought to publish an abstract of this theory,

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beginning, as was the case in our conversations, with the principal phenomena which determine the task of the geologist, as well as the point from which he ought to start, in order that he may remain within the bounds of known causes; limiting myself afterwards to extracts from those parts of my theory, the proofs of which are established in my works:-this, you observed, to naturalists acquainted with them, would be sufficient in others it might serve to excite the desire of employing their attention on this important subject.

1. Geology is principally distinguished from Natural History, inasmuch as the latter is limited to the description and classification of the phenomena presented by our globe in the three kingdoms of nature, whilst it is the business of the former to connect those phenomena with their causes. Geology embraces, therefore, the whole extent of what we can acquire of natural knowledge, since our observations on the earth constitute the only true sources of all that knowledge. Astronomers, for example, could have taught us nothing concerning the causes which operate in nature, merely by determining, as Kepler did, the laws by which large bodies move through space for if the cause of the fall of bodies on our globe had not conducted Newton to his theory of gravitation, we still should have been ignorant of the great laws of motion, the influence of which in nature is so general. Herschel, by his extraordinary skill in observation, has doubtless made great discoveries respecting the resemblances of other planets to the earth; no knowledge, however, could be drawn from thence of their past states, had not our studies on the

earth given rise to natural history, chymistry, staticks, and thereby revealed the great outlines of the history of our globe, which, by analogy, may be transferred to them. In vain, above all, would light have given us knowledge that an universe exists; this great assemblage of bodies would have been mute to us, as to its causes, had not the progress of observations and experiments upon our globe, discovered to us, in light itself, a substance capable of various combinations with other substances; and one without which all the other causes of the chymical affinities, those causes which, in the greatest part of the operations on these globes, have the most considerable influence, would be totally without effect. Such then is that geology, which is not merely nominal; it consists, as I have said, in the knowledge of the causes which have acted, and still act upon this earth; and thus it is that geology embraces all the knowledge we can gain of nature; as, on the other hand, there can be no real knowledge respecting nature,-in as far at least as depends upon mere human researches,— without an attentive study of all the terrestrial pheno

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2. Why has the earth any mountains ?-Such is the question from which I shall here set out, as, in my own private researches, which have never been intermitted, I set out from it forty years ago; and, before I can resolve this question, I shall have run through the whole field of natural knowledge, as far as I am master of it.

3. Why are there pyramids in Egypt ?-This is a question which the antiquary puts to himself with some hope of finding the solution, because he sees

some data to set out from: now the whole course which he pursues respecting these edifices, marks out that of the geologist on the subject of our mountains, and of our continents, the bases that support them.

4. The entire mass of our continents is composed of strata, similar in this respect to the regular courses of stones in our buildings. A succession of strata indicates a succession of time for their formation; and the change from one species of stratum, to another species placed upon it, indicates a change of cause. Thus is the mass of our continents the product of successive operations, during which the producing causes have undergone successive changes.

5. We see, moreover, that many of these strata contain the remains of animals; and that in some successive strata these organized bodies are of different species. By this we judge that some considerable length of time was necessary for the formation of these strata, both on account of the succession of individuals of the same species of animals in some of them, and also on account of the change of species, in the same places where the former are buried.

6. By much the greater part of the organized bodies found in our strata consists of the remains of marine animals, and some of these are even found in all the classes of strata, which contain other kinds of bodies not belonging to the mineral kingdom; so that all these strata have been formed beneath the waters of the sea. Nevertheless, these other bodies are remains of terrestrial animals and vegetables. Whence proceeds this mixture of terrestrial and marine bodies? Here is another characteristic of the causes which have operated within this period.