now existing, and that the only difference of consequence to be noticed is, the change of latitude in regard to some of the species; a circumstance not peculiar to the terrestrial animals, but which extends to numerous species of marine animals.

40. At length, then, I have arrived, through a series of geological monuments and physical causes, at the end of the sixth of those periods, into which I have divided the chain of operations which commenced from the addition of light to the other substances of which the earth is composed; fixing for the end of those periods, on the epoch when the sea was ready to abandon its first bed. I said at my entrance upon this discussion, that these six PERIODS bore a relation to the six DAYS mentioned in the first chapter of Genesis; nevertheless I have not adverted afresh to this idea (excepting in some particular cases) in the course of my exposition, because it is to stand alone. But when well-informed men shall come seriously to attend to the relation that subsists between the circumstances characteristic of each of these days, and what has passed on our globe in the periods corresponding, proved by monuments open to every one's observation, they will acknowledge that nature herself pays homage to that sacred and sublime history, which will receive very striking confirmations in the course of the period in which we live.

41. There is one main circumstance only of which these monuments give no evidence, namely, the appearance of man, in the sixth period; no human skeleton having been found in our strata; but from this we can draw no other geological consequence, independently of the Mosaic narrative, except that

men, if they existed then, had not passed, as the animals and vegetables had, into such islands as were subject to submersion; that they had remained on the ancient continents, and that they were destroyed with them in some succeeding revolution in which those continents suddenly sank, so as that the sea overflowed that portion of the globe, and abandoned its ancient bed, thus become our present continents. This shall be the subject of my next Letter; and when I shall come to point out the astonishing agreement of that catastrophe with the circumstances of the deluge as described by Moses, I shall particularly show that the absence of human reliquiæ from our strata, is in itself a very important phenomenon.

LETTER V.

Birth of our Continents-Proofs of the little distance of

that epoch.

SIR,

Windsor, July 1, 1794.

THERE exists no longer any doubt amongst naturalists that at the period of the birth of our continents, they were, and had been, for a long time, the bed of the sea; so that the principal object of geology is to explain," how the sea, after having been once higher than our continents, comes now to be depressed below them."

1. I have not, in these Letters, reverted to that question, "whether this important change that has happened on the surface of our globe has been produced gradually, or by a sudden revolution," because I have fully discussed it in my Letters on the History of the Earth and of Man, where I have proved, as well in answer to those systems that are founded on gradual causes, as in a general way, that the birth of our continents has not been gradual, but sudden ; and this is what has been also admitted by two of the most distinguished geologists of our time, M. de Saussure and M. de Dolomieu. But it remains to

determine the nature of this revolution; and I shall proceed first to cite some facts which clearly point it out.

2. We have seen that the entire mass of our continents is composed of strata, produced by the sea while it occupied this portion of the globe. These strata, which we may every where unequivocally trace, notwithstanding the various accidents they have undergone, extend every where down to the present sea, of which, after this revolution, they constituted the new boundaries. On this account I shall call

them continental soil.

3. As soon as the sea had changed its bed, the rivers were formed upon the new continents, and arriving at the sea, began to deposit at their mouths the mud they brought down with them: the sea also, agitating the sand in the more shallow parts, drove it back towards its shores by the action of the currents and tides. From these two causes, new lands began to be formed, which, contiguously to certain parts of the original coast, occupied successively the place of the water. These new lands are every where as distinct from the continental soil, as a layer of sand or gravel in front of a house, is from the house itself; their existence evidently proves that the level of the sea has had no tendency to rise since it has occupied its present bed; for, in this case, it would have successively overflowed either every where, or near certain coasts, the sediments that were deposited on its shores; whereas there are new lands upon every coast, or in its vicinity. If, on the contrary, the sea had had a tendency to sink, the new lands would necessarily have a regular slope towards it, by which we might

be able to measure the quantity of its depression since it occupied its present bed: but all the new lands, on every coast, of whatever extent they may be, are sensibly horizontal. This phenomenon, then, amounts to an absolute demonstration, that the sea has undergone no change in its level since it has occupied its present bed.

4. But before the sea occupied this bed, it covered our continents, and thus existed at a much higher level. What barriers could then retain it? It was impossible they could be other than lands more elevated than itself, which consequently occupied the place where the sea now is, and we know certainly, from the quantity of the remains of vegetables and terrestrial animals, which have been buried in our strata while yet under the sea, that there did at that time exist such lands. Thus, in order that the sea should have retired from the surface of our present continents, other continents, which before served it for a barrier, must necessarily have sunk so as to form the basin which it at present occupies.

5. This is a necessary consequence of the above facts, and its evidence does not depend on our determining how this revolution happened; but we shall soon discover it, by continuing to pursue the train of causes established in my former Letters, of which I shall, in few words, recall to your recollection such parts as the subject requires.

6. The state of disorder in which we find all our strata, could have been produced only by considerable and repeated subsidences of the greater part of their mass, at eras marked by their monuments. These subsidences of the bottom of the ancient sea could