what is comprehended in this most interesting study. Of its handmaid, mineralogy, we shall say nothing; because we have not room to say one-tenth of what we would willingly offer on the subject of geology alone. One observation, however, it is worth while to make in the outset. Of all exercise, exercise in the open air is the most delightful, the most interesting, the most healthful. With mineralogy, geology and botany, every mile of every road-every hill and dale, every mountain and valley-in every country, in every climate-cultivated, or waste and wild-affords reasonable expectation of something worthy the attention of a man devoted to these sciences. Where ignorance sees only a rough, mishapen mass of rocks and stones, or a plain overgrown with weeds, knowledge finds food for contemplation, and additions to his store. No journey can be uninteresting to such a traveller; hardly any road can be bad; the enticement to pursue these studies out of doors, is constant and all-powerful; and the pleasure in the pursuit as well as the attainment, is peculiar to the objects that excite the attention of the votary of science. If no more could be said in their favour, surely this of itself is enough.. Our present business is with GEOLOGY. This science comprises the present appearances of the strata that compose the crust of the globe, whereon man and all living creatures, animal and vegetable, live, move, and have their being. From present appearances, we deduce the history of these strata and their inhabitants, for many thousands of years anterior to the present. Geology also includes the order of succession and of time in which these strata have appeared, the phenomena that characterize them, and the uses to which this mass of knowledge may be applied. It is, in fact, the Palaiology of nature; memoria temporis acti. The rocks and stones that constitute the strata of the earth's surface, or that visible and habitable crust that envelopes the interior of our globe, is not a confused mass of heterogeneous materials thrown together lawlessly and irregularly, but the various strata, and the groups and connected series of strata, called formations, have been placed where we find them, according to certain laws of composition and successive deposition, which enable us to reason and draw conclusions from these circumstances of common existence, and apply the conclusions drawn, for instance, from the granites of South-Carolina, Virginia, Massachusetts and Maine, to the granites of Italy, of Sweden, of Canton, and of Canada. For even hand-specimens of granite in South-Carolina and New-Hampshire, are so similar to the same rock at Auvergne, in central France, and Can ton, in China, that neither ignorance or knowledge could tell à priori, from what quarter of the globe they respectively came. Geology, as a science, is founded on those observations which have furnished abundant evidence, that in the strata composing the crust of our earth, there is in every country and in every clime, Regularity of succession. Similarity of mineralogical composition. Similarity of fossile inhabitants of former oceans. Similarity of fossile plants imbedded in the rocks and soil. Similarity of fossile amphibious animals. Similarity of terrestrial herbivorous animals; and finally, Similarity of carnivorous animals; of which the last is MAN. These circumstances characterize each group of strata over the whole earth, formed or deposited previous to the last great deluge (or, as we rather hold it, succession of deluges) which preceded the appearance of the animal, man. Further-wherever members of the succession of strata are wanting, as the case frequently is-wherever disruptions, displacements, transportations and alterations in the succession of strata, take place-wherever rocks are thrown irregularly over others, out of the usual series of succession-these apparent anomalies can almost always be accounted for, from volcanic action in early times, and the earthquakes, upheavings, disruptions, deluges and cataclysms, that for so long a period rendered the surface of our globe an unsafe habitation for the human race. Werner of Freyburgh, during many years, studied the mountains and the strata in his own neighbourhood; he remarked and noted the characters that distinguished them, and the order of succession in which the strata appeared. The best view of his system may be found in the third volume of Jamieson's Mineralogy, first edition. Let any man start from Philadelphia and journey on towards Pittsburgh, and he will see Werner's succession of rocks under his eye the whole way. Take Arrowsmith's map of the United States, fix a pin and a string at Pittsfield in Massachusetts; stretch it in a line north-east and south-west, and the primitive limestone will be cut by that string through Whitemarsh, fourteen miles from Philadelphia, and thence all the way along the primitive limestone, through South-Carolina, into the same stratum in the Choctaw country. Do the same, beginning at the second fork of Sinnamohoning, in Pennsylvania; carry your string to the place marked "salt," in that map, in a south-west direction over the Mississippi: that line will mark very nearly the south boundary of the salt district of the United States. It is manifest, therefore, as to these continuous strata, through a district so extensive, that they must have been formed and located under one and the same general law of composition, formation, deposition and succession. Geology, therefore, having for its object the laws which have regulated the formation, location, deposition, succession and characteristic concomitants of the strata of the earth, is assuredly as much a science, as optics, astronomy, chemistry or botany; and the time expended on its acquirement is not, as some imagine, thrown away. All this is confirmed, if confirmation were needed, by the papers of Mr. Colebrook and Mr. Frazer, in the 1st volume of the 2d series of the Geological Transactions, where the corresponding features of corresponding strata, even the Basalts and Traps of volcanic formation in India and in England, leave no doubt, that in both regions, the strata have been subjected to the same general laws, and exhibit the same structure and the same concomitants. This globe is an oblate spheroid; 7927 miles in diameter at the equator, and about less in the other diameter. The precise flattening at the poles is not yet ascertained: and if Captain Sabine's observations be well founded, the pendulum will not furnish an accurate proportion. The crust of the earth (the rind of the orange) is of a thickness not yet accurately estimated, nor have means been yet imagined by which this can be effected. The deepest mine known, Truttenberg in Bohemia, is but 1000 yards in depth. The depth from the surface into the crater of a volcano, does not seem great; but we know not yet the circumstances that would aid or would obstruct our arriving at this knowledge. Pallas, travelling across the outbreakings of primitive strata, calculated the thickness of the primitive formations at 21 miles. Dr. Cooper and Mr. Lardner Vanuxen, from the same mode of measurement, seem to be of opinion that the thickness of the primitive range is nearly three times that amount. Van Humboldt somewhere estimates the granite at about 1 miles. All this shews not our knowledge, but our ignorance of the question. "As the rind to the orange," seems a comparison not very much out of the way, until we know more, and more accurately. It is the surface only that is destined to support life. Of that surface, not more than twelve feet in depth is thus occupied. The Locustæ Septembrecin were traced in their passage out of the ground near Germantown, in 1793, to that depth. (Dr. Barton.) Of living beings, animals alone possessing a nervous apparatus, have sensation. The whole family of plants, destitute of nerves, are, for that sufficient reason, destitute of feeling or sensation; and, of course, of voluntarity, notwithstanding some doubtful appearances. The internal mass of the globe, under the crust of the earth, is, and probably always has been, in igneous fusion. appears, This 1st. Because every known specimen of that internal mass, throughout all ages, such as the lava streams of volcanoes, were ejected in igneous fusion. 2ly. Because the rotation of the earth on its axis, to produce the oblateness at the poles, must act on a fluid mass. This fluidity is the fluidity of igneous fusion alone: aqueous solution is out of the question. 3ly. Because the experiments made by Cordier, as well as those collected by him, shew, indisputably, an increase of temperature as we descend. 4ly. The fossiology of the northern regions, vegetable and animal, forces on us the conclusion, that the temperature of the earth in those regions, and the climate, were much warmer formerly than at present, inasmuch as there is no sufficient reason to suppose that the tropical plants and animals found inhumed in Siberia, were carried thither from a distance by any force now known to us. That the surface of the earth and the northern climates have grown colder since the last series of deluges, is reasonably concluded from the tropical plants and animals imbedded in northern strata; and which appear to have lived and died in the locality where they are found. The fossile shells of a crowd of authors, the invaluable works of Cuvier and Brogniart on fossil animals, and the Prodrome of plants of M. Brogniart, furnish abundant proofs of this. From the observations presented to us by Sir Isaac Newtonfrom the experiments and calculations of Dr. Maskelyne, Dr. Hutton, and Mr. Playfair, on the hill Shehallien-from the experiments made by Mr. Cavendish, with the apparatus of Mr. Mitchell and M. Conlomb-there is sufficient reason to believe, that the specific gravity of the globe of the earth is to that of water, at least as 5 to 1; nearly double that of the generality of rock-minerals, of which the crust of the globe is formed. The specific gravity of the interior will, doubtless, be increased by superincumbent pressure, and as the specific gravity thus increases, caloric of temperature will be given out, according to the known laws of the combination and disengagement of latent caloric. Whether this will suffice to account for the great heat of the interior on the theory first advanced by Dr. Cooper, will VOL. VI. NO. 12. 37 admit of great doubt. We want more facts. Whether the earths are metalloids in the interior, and become oxyds by the contact of admitted air and water, as Sir H. Davy once supposed, we have no means at present of ascertaining. Granting the igneous fusion of the interior mass, a fact hardly deniable, the occasional admission of water, the decomposition of that water into oxygen and hydrogen, and the violent agency of steam, will abundantly account for volcanic ejections, earthquakes, disruptions, displacements, deluges and cataclysms. These must have been very violent and very frequent during the early part of the earth's existence, and while the crust of the earth was comparatively thin; and they continued in dreadful succession, even within the reach of human observation and tradition. The two hundred volcanoes known to be, and to have been in occasional activity within the period of historical evidence, serve as spiracles to the vapours and gases which would otherwise produce the same kind of devastations to which the surface of the globe furnishes so many indubitable attestations. We say two hundred, instead of one hundred and seventy-three, enumerated by M. Arago, Daubeney and Scrope, because there is as yet no complete and accurate account taken of these outlets of danger in the Pacific and in the Eastern Archipelago. The present surface of the earth is occupied in the proportion of two-thirds by water. The depth of the ocean has not yet been satisfactorily ascertained. Captain Parry, at 100 leagues from shore, in N. lat. 68 24', long. 63 8' West, from Greenwich, found no bottom at 1020 fathoms. Along the Eastern coast of America, at 100 leagues from shore, the depth is from 50 to 60 fathoms. The theory of tides seems to require that the average depth of the Atlantic should be about three miles. In no instance have we reason to conclude that the greatest depth of the ocean exceeds four miles. The highest mountains of the globe do not reach five miles. A great part, perhaps the greatest portion of the present surface of the globe, has, at former times, been the bottom of the ocean. How happens this change to have taken place? What forces known to us could have produced it? There is only one solution of this problem possible. The bottom of the former ocean must have been raised by a force underneath, such as the action of water let into the igneous abyss, and suddenly decomposed or converted into steam. These upheavings do not appear to have been simultaneous over the whole earth, but to have happened frequently, first in one part, then in * Young's Natural Philosophy, vol. 1, p. 581. |