with new ingredients, thus occasioning a change in the nature of the precipitations-a change proved by the superposition of strata successively different. During these precipitations the expansible fluids themselves changed their nature, and gradually formed our atmosphere. De Luc likewise shows, from the theory of subsidence, that while the catastrophes which the strata underwent at different periods, demonstrate that caverns must have been successively formed beneath them, the important phenomenon that has given birth to geology, is explained, viz. the disappearance, at the exterior, of a great portion of the liquid which formerly covered the whole globe, at a level exceeding our highest mountains'. At the termination of the catastrophes, those cavities were nearly filled up by the masses of strata, which, as they sank, descended to the bottom. The stability of our continents was thus effected, and such vacant spaces alone remained as occasion the present phenomena of volcanic eruptions and earthquakes 2. For the caverns were not receptacles for

1 Letter V. § 6.

66

2 Letter IV. § 7. Of these phenomena a very satisfactory solution, in immediate connection with the leading features of the system, will be found in Letter IV. of this collection. See also Journ. de Physique, tom. xxxviii. p. 274; tom. xl. p. 451; xli. (part ii.) p. 227; and xlii. p. 235, (1793.) "There is," says M. de la Métherie, a very considerable number of volcanos which are at this day extinct. Large caverns must necessarily exist beneath the spots where they were once in activity." Journ. de Physique. The great earthquake at Lisbon, in the year 1755, which was felt at the same time in several countries of Europe, proves the existence, in that part of our hemisphere, of very deep and extensive caverns. Journ. de Physique, tom. xli. (part ii.) p. 329.

the liquid, but served as avenues for its further infiltration into the porous mass of the globe 1.

To discover any one particular cause of the disappearance of the liquid at the exterior, remarks our author in his xxxth Letter to M. de la Métherie, is of no avail towards serving as a foundation of a theory of the earth; all other geological monuments connect themselves with this fact, and require that its cause should explain them also. Accordingly the discovery of such a cause can result only from a long study, of all the principal geological phenomena, and all the laws of terrestrial physics. But the time, the labours, and the perseverance required by this study, are amply compensated by the light which the different phenomena reflect one upon another, a real light which alone can lead to a geological system of which the bases are found in nature 2.

SECTION VIII.

Moral importance of Geology.

At the conclusion of the sixth Letter occurs a brief recapitulation of the motives that induced De Luc to apply himself to geological researches. It is evident that no subject is calculated to awaken a more general interest than that which connects itself with the history of our planet, since the consideration of physical events which relate to the globe inhabited by man, necessarily involves the consideration of the history of man himself, and may serve to confirm what

1 Journ. de Physique, tom. xlii. p. 235, (1793.) 2 Journ. de Physique, ibid. p. 234.

a venerable tradition has from the earliest times established among mankind, and what it most concerned them to know, viz. their origin, their duties, and their destination. Hence the study of the monuments of the revolutions which the earth has undergone, together with their causes, assumes a great moral importance 1.

Investigations into the physical history of the globe having naturally called back men's attention to that history, as it is contained in Genesis, and also to that of the human race, with which it is connected, it was soon inferred, that, if geology were contrary to Genesis, the latter must be fabulous. "This is a consideration," says the author, "which I offer to those, whose profession it is to teach and defend revealed religion. The weapons by which it has been attacked have been changed, and our modes of defence must be adapted to the arms of its assailants. They now attack it through geology; which therefore becomes a science as essential to theologians, as the study of learned languages, or of those ancient arguments, which are already much neglected in the present times, and which must henceforth derive their chief support from the very science, through the medium of which, under the pretence of an appeal to facts, it is attempted to set them aside "."

Although the first geological systems contrary to revelation have fallen to the ground, in consequence of the increase of knowledge, the premature attempts of those who have written in its defence, have likewise produced various chimerical theories. "The adver

1 Letter VI. § 51.

2 Elementary Treatise, § 6.

saries of Genesis," remarks De Luc, "by overthrowing those groundless systems, imagined that they triumphed over Genesis itself. While geology, therefore, was in its infancy, philosophers should have contented themselves with pointing out the errors of the anti-mosaical systems, for which the state of the physical sciences was sufficiently advanced to have readily furnished them with the means: and they should not have hazarded theories, before they had taken every requisite precaution to fix them upon an immoveable foundation 1."

1 Ibid. § 9. Mr. Lyell asserts that De Luc "imputes the failure of former geological systems to their having been anti-mosaical," p. 68. It is obvious that in the passage to which he adverts (Elementary Treatise, § 8.) Mr. L. has misapprehended the meaning of our author, who simply states that the geological systems which had been published contrary to Genesis, had "fallen in consequence of the increase of knowledge," and reproves the levity and imprudence of such attacks on that, which a sublime tradition had established among men. De Luc more particularly alludes to the writings of certain foreign naturalists, such as the German work entitled, Die Geognosie nach chemischen Grundsatzen, by Dr. CHARLES SCHMIEDER, member of the Society of Halle. The general principles and cosmological system of that author are investigated and combated by De Luc in his Abrégé de Principes et de Faits concernans la Cosmologie et la Géologie. (1803.) Another publication, by Prof. Poтт, of Helmstedt, called forth the animadversions of our author. professor," he observes, "wrote a work entitled 'Moses. logist,' he uttered, without perceiving it, a great truth; for if Moses unfolded, before geology existed as a science, truths which men were unable of themselves to discover by any other means, he could do so only by divine inspiration." Mr. Lyell will thus find, contrary to the opinion he expresses, that there are writers who have openly or covertly, "been guilty of endeavouring by arguments drawn from physics, to invalidate scriptural truths." p. 68.-" Voltaire, d'Alembert, Diderot, &c." observes De Luc, in a letter written

"When the

....

no Geo

The venerable author further states that he has devoted fifty years of his life to these investigations'; and he makes the pious and affecting acknowledgment, that in consequence of the conviction which they produced in him of the truth of revelation, he "found the reward of his labours in an inward satisfaction, which the vicissitudes of his life, although not inconsiderable, have never been able to destroy."

Anxious, from the deep impression which he ever entertained of the importance of the subject, to excite a more general desire after geological enquiries, the author, in his preface to his Travels in the north of Europe, makes, with that view, some valuable observations, the substance of which will furnish an appropriate conclusion to the present introductory remarks:

:

"The history of our globe, like every other which relates to past time, can be traced back only by monuments. It is thus that the histories of nations have been compiled; but of those the most ancient to Mr. EMERY, the editor of the French edition of the present work, "addressing the imagination and the feelings, were especially calculated to mislead the unthinking; but minds capable of any reflection, and of maintaining principles of their own, would have escaped their influence had not Buffon, Maillet, le Cat, and other natural philosophers of their class, appeared to assure the world that every thing in nature was opposed to the Mosaic history, the base on which revelation is founded." Mr. BABBAGE, Lucasian Professor of Mathematics, in the University of Cambridge, adverts in like manner to the "geological speculations which have been adduced as inconsistent with the Mosaic history." Reflections on the Decline of Science in England, p. 137.

1 Letter VI. § 51. With a persevering activity seldom witnessed at such an advanced age, De Luc carried on his geological researches for upwards of fifteen years after the date of that letter.