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VOLUME the SIXTY-FOURTH.
Lettres Phyfiques et Morales fur l'Hiftoire de la Terre et de l'Homme, &c.-Letters Philofophical and Moral concerning the History of the Earth and of Man; addreffed to the QUEEN of Great Britain, by J. A. DE Luc, Citizen of Geneva, Reader to her Majefty, F. R. S. Correfpondent Member of the Royal Academies of Sciences at Paris and Montpellier, in Five Volumés Ɛvo: Hague, 1780. l. 1OS. Sold in London by Elmfly, &c.
WE E return with pleasure to this excellent work, though
we can only give our Readers an imperfect and general idea of the riches it contains. In a former account of its valuable contents, we followed the ingenious Author, in his analytical progress through a multitude of phenomena, and obferva tions founded on them, to the great revolution that produced the prefent ftate of our globe t,-the fea's changing its bed and covering the ancient continents, after having previously covered
After having afcertained this important event by an exact analyfis, M. DE LUC enters into a fynthetical examination of the refults of this inquiry, and gives us the phyfical hiftory of the earth from its primordial ftate to the revolution that occafioned its prefent aspect. In defcribing the changes which the furface of the earth has undergone, he fets out with this position, that when the fea covered our continents, it had a mountainous bottom, which neither the waters nor any known cause had formed, and which therefore our Author calls primordial. Some of these
Vid. Appendix to the 62d volume of our Review, p. 527. + See the Article referred to in the preceding Note.
APP. REV. Vol. Ixiv.
mountains arofe above its furface, and formed iflands: thefe islands and the ancient continents were fruitful, and were peopled the ancient fea, which covered the modern ones, had its tides, its currents and tempefts. Thefe powers, acting upon the foft matters which are known to have formed the ancient bottom of the ocean (when it covered our continents), produced accumulations of calcareous fubftances, more or lefs mixed, in process of time, with marine bodies. The rivers, in the mean while, carried to the sea scattered fragments of terrefrial vegetables and animals; the fea, itself, washed them off its coasts; and these materials, tranfported by its currents, became a fecondary foil or ground upon its primordial bottom. Our Author fhews, how fires kindled and elaftic fluids (formed by the fermentation, which the waters, filtrated through. these accumulated bodies, produced) made various openings in the bottom of the ocean, from whence proceeded torrents of liquefied fubftances and lava, which gave rife to the volcanic mountains, obfervable on the furface of our continent. The cavities, produced in the interior parts of the earth by the eruption of the fe liquefied fubftances, affumed the form and direction of galleries, and thus undermined the bottom of the fea to a confiderable extent. (We abridge and refer the Reader to the work itself for the details and proofs of all this, which are abundant and fatiffactory.) Thefe excavations, when large quantities of elastic fluids were engendered at once, produced earthquakes, which hook even the mountains, and occafioned in them chinks or openings. Thefe chinks were prevented from clofing by the ruins that fell into them from the fides of the mountains, and, being afterwards filled with heterogeneous fubftances, in whose compofition the fea-water and fubterraneous fire may have concurred, exhibited veins, in which, fince they have been dried, the filtration of the waters has produced a variety of changes, of which many are obfervable.
The bottom of the ancient fea (which covered our continents before the Deluge) had under it caverns, whofe vaults, being thinned and impaired by the excavations made by fubterraneous fires, were either pierced, or fell in from time to time. Hence the gradual finking of the fea beneath its level, from the entrance of its water into the caverns, which diminished the influence of the tides on its undulations; while, from its bottom, being traversed by fecondary elevations, confiderable changes enfued in the direction of its currents, and confequently a great variety in the height, pofition, and nature of its accumulations. It is very remarkable, that the fea, after having made great acquifitions of calcareous matters in the first period of its operations, ceafed almost every where to accumulate this kind of fubftances, and fubftituted vitrefcible matters in their place, long before it with
drew from our continents, and in a third period had fcarce any thing to transport from one place to another but marl, clay, and fand, the latter of which, more especially, it fpread both on its primordial bottom, and alfo on the fecondary ones formed by its own preceding depofits.
The continents, which exifted in a ftate of population and fertility while the ancient fea covered ours, though they did not form a folid mafs, but were, properly speaking, vaults, which covered immenfe caverns, maintained their elevation above the level of the fea by the strength of their pillars, which, being of primordial matter, were folid and stable. But the particular changes, which the fubterraneous fires produced in the bottom of the ancient fea, opened paffages for its waters into the interior of the earth, and thus introduced them into fome of the caverns, which were covered by the ancient continents. The fermentation, produced by this irruption, fhook the pillars of the primitive earth, which finking into its caverns, the continents difappeared their furface defcending below the level of the fea, made room for the waters to fpread themselves on every fide e; but as the declivity was gentle, and the borders of the bafon which emptied itfelf were unequally elevated, the inundation, though rapid, was only fuperficial, and neither put in motion, nor drew after it, the fandy bottom, which ftill remains entire in our continents.-At the end of this firft part of the great revolution, the fea covered all the globe, except the islands of its ancient bottom, which increafed in number and magnitude, but continued still separate, until the weight of the water, added to that of the fuperior vaults, crushed the inferior ones, and deepened more and more the new bed of the ocean; fo that, at laft, by a motion rapid though not violent, all the waters withdrew from their former bottom, and left our continents dry.- -The extinguifhed volcanos on our continents are a ftanding proof of the folidity of M. DE Luc's fyftem; as alfo the fituation of the volcanos actually known, which are all in iflands, or in places near the fea. As foon as our continents were delivered from the waters, the fermentations which they produced in combination with fire and other phyfical agents, ceafed; these agents, having no more that weight of water to raife by which they fhook the vaults of the galleries, made fome explosions indeed, which difperfed the ruins of the fhattered ground, and covered fome parts of our continents with a difcharge of primordial fones, but their efforts were exhaufted for want of aliment, in galleries, whofe vaults were pierced, instead of caverns, where there would have been oppofition and materials to foment their activity. The old volcanos were therefore extinguished (and their numbers were prodigious, as we fee by the late important publication of M. Faujas de St. Fond), and new volcanic erup
tions arofe in the new bed to which the waters withdrew. The Grecian, Sicilian, Indian, and Northern Islands may be alledged as illuftrations of this history of the firft of the two periods into which our Author divides that part of the duration of our globe, which is acceffible to our inquiries by the phenomena it exhibits.
Having treated the ancient hiftory of our globe, fo far down as the great revolution (or Deluge) that produced the continents we actually inhabit, our Author proceeds to its modern history, which takes in the period between that revolution and the prefent time. Here our ingenious inveftigator has ftill more ample fuccours and furer guides, as all the caufes that began to operate upon our globe, after the formation of our continents, continue till their action and influence. By the view of these an estimate may be made both of their paft and prefent effects, and this view will enable the fagacious inquirer to meafure, with no fmall degree of precision and probability, the time that has elapfed fince thefe caufes began to operate.-Accordingly, our Author enters into this investigation. He obferves, that the two general fources, from whence the new earth (our prefent continents) received the germs of fertility and population, were the plants, feeds, and animals, that the fea, during the great revolution, carried off from the finking continents, and which, driven by the winds and waves, were thrown upon the ancient iflands (our present mountains), in proportion as they rofe out of the departing ocean, and afterwards upon the borders of the new continents. Thefe depofited materials of vegetation continually accumulated-the turbification* of vegetables in low grounds of a fandy bottomthe diminution of fertility on the high mountains from the accumulations of fnow and ice, which conftantly increase (and would have already crufted over thefe mountains entirely, if the antiquity of our globe was fo remote as fome philofophers pretend)-the waftes of the mountains and the talus formed by the mouldering parts of them that fall from time to time and the fubftances which the rivers carry in their current to the fea;— thefe are the five claffes of phenomena which M. DE Luc employs, ingeniously, to prove the recent origin of our continents, and to fhew that the present state of the earth's furface is not of a very ancient date. This is farther confirmed, as our Author obferves, by the hiftory of mankind, whofe deftination it is to cultivate the earth and to study nature, and who, nevertheless, have hitherto made but fmall fteps towards the accomplishment of thefe important purposes.
After having confidered the phenomena which afcertain the
* We have adopted from the French this term, which expresses the change of vegetables into a turfy earth.
great revolution above mentioned, M. DE Luc examines thofe which characterise in a more particular manner the nature of that revolution, and fhew, that it was effectuated by the paffage of the fea from one part of the globe, which it had formerly covered, to another part, which it had not covered.'. The marine foffils, contained in the mountains, hills, and plains of our continents, and which characterife animals, of which fome claffes have not, as yet, been difcovered in any fea, and others that have only been obferved living in feas at a great distance, are employed by our Author to prove this paffage, as it has been already defcribed.-The remains of a great number of terrestrial vegetables and animals are found in our continents (inclosed in the fubftances which were accumulated by the fea when it formerly covered them), of which animals a very confiderable number are different from all the claffes of living animals known in our regions; while others belong to claffes that only exift in the oppofite hemifphere, and others again have not been, as yet, discovered living in any part of the globe. All thefe circumftances are ingenioufly brought to fhew, that there exifted populous and fertile continents during the period when ours were covered by the fea.
That fragments, fkeletons, and remains of animals, which at prefent live only in the fouthern regions, fhould be found in the bowels of the earth in the northern parts of our hemisphere, is indeed a very fingular phenomenon. M. De Buffon accounted for it by his whimfical hypothefis of the original fiery fluidity of our globe, and its gradual refrigeration, which produced the removal of feveral claffes of animals towards the Equator, which had formerly inhabited the regions of the North. This fyftem, which was a pretty entertainment for the beaux and belles of Paris, intoxicated fome people from whom more wisdom might have been expected; and many readers were so amused to see the elephants and rhinoceroffes galloping towards the Equinoctial, that the epochas of Nature were almoft univerfally applauded, and warmly defended. But they have had their day, like the elephants of the North, and are now contracting the influence of that refrigeration which their inventor attributes to our terreftrial globe. Our Author has not fuffered them to cool gra dually, or to die away of themselves: he has given them a finishing, a deadly blow, from which it will be impoffible for all the magic of M. De Buffon's pen to recover them. The Letters in which he examines M. Buffon's hypothefis, and M, Mairan's notion of a heat peculiar to the earth, on which this hypothefis is founded, are fingularly interefting and inftructive; and fhew in reality that M. DE Luc is a master in the fcience
See the Appendix to Vol. Ixi. of this Review,