principle, that has yet been presented to the public. Indeed, its unreasonableness and extravagance are so great, that it seems to have attracted but little respectful attention among any class of philosophers.

SECT. XX.

THEORY OF KIRWAN.

THE last person to be mentioned, as having adventured in this ample field of speculation and inquiry, is Mr. Kirwan. This gentleman with that learning which has enabled him to prosecute his numerous investigations in so enlightened a manner, with that judgment and penetration which render his inquiries so valuable, and with that spirit of patient and accurate observation which is so indispensably necessary to a successful development of this subject, has framed a theory of the earth, which is perhaps the most rational and probable extant.*

Mr. Kirwan believes that the superficial parts of the globe were originally in a soft liquid state, proceeding from solution in water heated at least to 33°, and possibly much higher that this menstruum held in solution all the different earths; the metallic, the semimetallic, the saline, and the inflammable substances: that in this fluid its solid contents coalesced and crystallized, according to the laws of elective attraction; that these were deposited in strata according to the predominant proportion of the ingredients: that by this crystallization of these immense masses a prodigious quantity of heat must have been generated, and increased by the decomposition of the water intercepted in the precipitated ferruginous particles, and by the disengagement of inflammable air, even to incandescence; the oxygen uniting with the inflammable air, and bursting into flame; that this stupendous conflagration must have rent and split to an unknown extent the solid basis on which the chaotic fluid rested: that from the heated chaotic fluid must have been extricated the oxygen and azotic airs, which gradually formed the

* Geological Essays, by Richard Kirwan, Esq. F. R. S. &c. 8vo. 1799.

atmosphere that from the union of oxygen with ignited carbon proceeded the carbonic acid, the absorption of which, as the chaotic fluid cooled occasioned the crystallization and deposition of calcareous earth. Mr. Kirwan also believes, that the immense masses thus crystallized and deposited formed the primitive mountains; that the formation of plains took place from the subsequent deposition of matters less disposed to crystallize in the intervals of distant mountains; that the level of the ocean gradually subsided, leaving large and elevated tracts of land uncovered; that the creation of fishes was subsequent to the emersion of the land; that after this retreat of the sea, the earth soon became covered with vegetables and peopled with animals, being in every respect fitted to receive them; that the gradual retreat of the waters continued until a few centuries before the general deluge; that this event was occasioned by a miraculous effusion of water both from the clouds and from the great abyss-the latter originating in and proceeding from the great southern ocean below the equator, and thence rushing on to the northern hemisphere, spreading over the arctic region, and descending again southward; that during this elemental conflict, the carbonaceous and bituminous matter ran into masses no longer suspensible in water, and formed strata of coal; and that other substances, by the combination or decomposition of their respective materials, formed various other kinds of mineral bodies, as basaltic masses, calcedonies, spars, &c.

That the inequality of declivity exhibited by the sides or flanks of mountains, in every part of the globe, had any regard to the points of the compass, seems to have been first remarked by the celebrated Swedish geologist, Tilas.*

He supposes that this fact is connected with the original structure of our globe; that it proves that mountains are not mere fortuitous eruptions (as some, within a few years past, have confidently advanced) and that it furnishes a powerful argument in favour of the Mosaic account of the creation, deluge, &c.f

BUT, although there has been in modern times (as appears from the foregoing pages) a wonderful variety of * See Memoirs of Stockholm for 1760.

See Transactions of the Royal Irish Academy, vol. vii

fanciful productions, under the name of geological theories, we are by no means to imagine that nothing has been usefully done in this department of natural history. Amidst all the splendid rubbish with which it has been incumbered, some precious treasures have been brought to light. Amidst the speculations which have darkened counsel, large additions have been made to our knowledge of this important subject. These may be briefly summed up in the following particulars.

The materials for the formation of a correct and rational theory of the earth have been greatly augmented during the last age. Enlightened mineralogists, practical miners, and patient chemical experimenters, have been engaged, throughout the century, in making accurate observations; in visiting foreign countries; in exploring the bowels of the earth; in comparing the strata of every portion of the globe; in examining their form, direction, extension, and connexion; in analyzing their component parts; and in collecting a multitude of facts, which have all tended to throw light on the origin and history of our planet. By means of the useful discoveries which these inquirics have made, we are furnished with weapons for beating down false theories, and with information enabling us to pursue our investigations further, and with more advantage.

Difficulties have been lately removed which were once supposed, by some, to militate strongly against the possibility of a general Deluge. Early geologists, for want of accurate information, supposed that all the waters of the globe were not sufficient to cover the whole earth to such a depth as the sacred historian describes. It was asserted that the mean depth of the ocean, did not exceed a quarter of a mile, and that only half of the surface of the globe was covered by it. On these data Dr. Keil computed, that twenty-eight oceans would be requisite to cover the whole earth to the height of four miles, which he judged to be that of the highest mountains; a quantity, which, at that time, was utterly denied to exist. But further progress in mathematical and physical knowledge has since shown, that the different seas and oceans contain at least forty-eight times as much water as they were supposed to do, and much more than enough for the extent ascribed to the deluge in the sacred history.*

*Kirwan's Geological Essays, pp. 66, 67.

While difficulties which were supposed to render the deluge impossible have been removed by the investigations of modern philosophers, many facts have been, at the same time, brought to light, showing the probability, and even certainty, of that mighty inundation. In every valley and mountain, support for revelation has been found. (See Appendix No. 3.) Marine shells have been discovered in situations so elevated, and under circumstances so remarkable, as to prove that they were left there by a flood extending over the whole globe; and what confirms this conclusion is, that shells peculiar to different shores and climates very distant from each other have been found in promiscuous heaps, plainly showing that they could have been brought together only by an extensive inundation. The bones of elephants and of rhinoceroses have been found, in a multitude of instances, far distant from the regions in which they are found to live, and where, from the nature of the climate, they could never exist in the living state and between the climates which they might have inhabited, and the places, in which they are now found, too many mountains intervene to suppose them carried thither by any other means than a general deluge.* The most patient and accurate examinations of detached mineral substances, and of the strata of the globe, which late inquirers have made, afford every reason to believe that the earth was for a considerable time wholly overflowed with water. And, to crown all, as voyagers and travellers have explored new regions of the earth, they have found, every where, the indications of geological phenomena confirmed and supported by the notices of tradition. Accordingly, it is very remarkable that a great majority of modern theorists have embraced the Neptunian doctrines; and even such of them as rejected the Mosaic account of the deluge have been compelled to seek for other means of immerging the present continents in the ocean.

Finally, the researches of modern geologists have given abundant confirmation to the sacred history, not only with respect to the general deluge, but also with regard to the

age

of the earth.

*Kirwan's Geological Essays, p. 54, et seq.

NATURAL

HISTORY OF THE EARTH.

PART III.

SECT. I.

THE natural division of this globe of ours is into sea and land; about three-fourths of it being occupied by water, although probably no where to a depth comparatively very considerable. The remaining fourth consists of land, elevated more or less above the level of the sea, interspersed in some parts with small collections of water, at various heights, and, in a few instances, somewhat lower than the surface of the main ocean.

The internal constitution of the earth is little known. The deepest excavations that have been made by human art do not exceed 2400 feet, or less than half a mile; which is a very short distance indeed when compared with the diameter of the earth, which is about 7947 English miles so that whatever lies below that depth is to us utterly unknown. The substances which have been extracted from those excavations are not in general of a nature different from those which in some particular places have been found immediately upon the surface. These substances are in general arranged in strata, variously inclined to the horizon, and of a thickness not very equal. Some indeed have supposed that they follow each other, in a certain order, almost throughout the globe; but this opinion appears to rest on slight foundations.

The mean density of the earth, deduced from the observations made by Dr. Maskelyne on the sides of Schehallien, an insulated mountain in Perthshire, is 41, rec