to complete the outer crust of a world, on which such an immense increase of surface had been instantaneously produced, there required to have been provided instantaneously an amount of solid rock to fill up the expansion which had thus taken place. Nor must it be supposed, that this difference of surface is the estimate at its full extent; for, were the inequalities occasioned by the continents and ocean beds, the mountains and valleys, and other flexuosities of surface, taken into account-the above being merely deduced from plane surfaces-the actual increase would be found to be infinitely beyond that which has been stated. It must, at once, be confessed, that the superficial extent of rock, instantaneously required to fill up this void, could not have been supplied from any resources residing in the stratified masses themselves. For there is no possible way, according to natural cause and effect, whereby a movement of the earth could have occasioned a spreading out of the strata over this enormous increase of surface; and, likewise, over that which has not been taken into account. It is said, "according to natural cause and effect," because, for wise purposes, the diurnal rotation of the earth was ordained to be the natural effect of causes instituted directly by the Deity, with power to produce, in sequence, that stupendous result as their first and chief effect; therefore, it is considered quite justifiable to adopt this language, without in the least attempting to limit the infinite powers of the Creator; but, on the contrary, while reverencing those attributes of Omnipotence, I look upon myself as authorised, in the present instance, according to the natural connection between cause and effect, to conclude, that not only was there no possible way whereby the strata could have been made to cover this extra surface; for the vertical positions, which most of them have assumed, would increase the embarrassment, were it attempted to bring them forward as sufficient for the exigency contemplated, it being well known, and readily admitted, that a plane of any given dimensions covers a greater concentric surface when horizontal than when tilted up into any angle whatever out of perfect horizontality. Some other phenomena must therefore be looked to for a satisfactory explanation of this difficulty; although it will lead us into rather a lengthened chain of reasoning, requiring the aid of various Theorems and their accompanying evidences, and the combination of truths which, perhaps, have never before been brought into juxtaposition; nevertheless the undertaking must be continued with patient perseverance, in hopes that it may ultimately lead to satisfactory results. SECTION IV. INTRODUCTION OF THE LIGHT; THE CONSEQUENT FIRST DIURNAL ROTATION OF THE EARTH; AND ITS DYNAMICAL RESULTS. WITH CHAPTER XVII. ITH reference to what was stated at the conclusion of the foregoing chapter, the first point to which the attention will now be directed, while endeavouring to establish it, is the relative insignificancy of the estimated thickness of the earth's outer crust, in comparison with its entire radius. With this view, let us, on commencing, read carefully the twenty-first Theorem, to be assured that there is such a thing understood among geologists as an "outer crust of the earth." In selecting evidences from among the numerous authorities for this opinion, I shall give what may be considered the expression of a pretty general one on this point, since Dr. M'Culloch takes it up with the intention of refuting it, when treating on "the depth of the strata beneath the surface.” "It has," he says, "been ignorantly made a matter of reproach to geologists, that they reason respecting the structure of an earth to which they have had no further access than by operations that ought to be considered but as scratches on its surface. It has been said that the highest mountains are but as dust, and the deepest mines but as invisible punctures on a common geographical globe."* "When we examine," observes Mr. Lyell, "into the structure of the earth's crust (by which we mean the small portion of the exterior of our planet accessible to human observation), whether we pursue our investigations by aid of mining operations, or by observing the * Geology, vol. i. p. 94. sections laid open in the sea cliffs or in the deep ravines of mountainous countries, we discover everywhere a series of mineral masses which are not thrown together in a confused heap, but arranged with considerable order; and even where their original position has undergone great subsequent disturbance, there still remain proofs of the order that once reigned." "Beneath the whole series of stratified rocks," says Professor Buckland," which appear on the surface of the globe, there probably exists a foundation of unstratified crystalline rocks, an irregular surface, from the detritus of which the materials of stratified rocks have in a great measure been derived-amounting, as we have stated, to a thickness of ten miles. This is indeed but a small depth in comparison with the diameter of the globe; but, small as it is, it affords certain evidence of a long series of changes and revolutions, affecting not only the mineral condition of the nascent surface of the earth, but attended also by important alterations in animal and vegetable life."t A recent popular work contains the following evidence respecting not only the assumption of the earth having an outer crust, but also its presumed thickness. It is given in reference to Part II. of Mr. Henessy's "Researches in Physical Geology," communicated to the Royal Society by Major Beamish; the part which interests us, at present, being Clause 2nd, which states that "By employing the values of the constants obtained in Section IX., it appears that the thickness of the earth's crust cannot be less than 18 miles, and cannot exceed 600 miles."‡ And still more recently, on this much-debated subject, the following hints transpire in the inaugural address of Professor Hopkins, at the last meeting of the British Association at Hull, when treating of the prevailing favourite speculations as to the internal condition and temperature of the earth : "Hence," says he, "the opinion adopted by many geologists is, that our globe does really consist of a solid shell not exceeding 40 or 50 miles in thickness, and an interior fluid nucleus, maintained in a state of fusion, &c. It might, at first sight, appear that this enormous mass of molten matter, enclosed in so thin a shell, could scarcely be consistent with the general external condition of the temperature of our globe; but it is quite certain that these are not inconsistent with each other, and that no valid argument can be urged against the hypothesis." § Principles of Geology, vol. iii. p. 8. + Bridgewater Treatise, vol. i. p. 42. Athenæum, p. 1068, Sept., 1853. If the estimated elevation of nearly 27,000 feet be thought unworthy of being taken into account, when estimating the diameter of the earth, neither is the mean thickness of the earth's crust comparatively worthy of notice. Thus we have come to one certain conclusion for determining the question at present under discussion. It is this: that, during the nondiurnal rotatory period of the earth's existence, the perpendicular distance, from the surface of the coal measures to the inferior strata which repose on the unstratified rocks, was so insignificant, in comparison with the radius of the earth, that, for any purpose wherein those two limits require to be adduced, they may be assumed, for all practical purposes, as equidistant from the centre of gyration. We must next endeavour to determine the relative densities of the several classes of rock, especially of the primary and older stratified masses, and of the more modern of the secondary formations, in order to institute a comparison between them; though it is somewhat difficult to arrive at this point with any degree of precision, for it seems hitherto to have attracted but little attention as a specific question; nevertheless there is abundance of evidence to prove, in a general way, the received opinion, that our globe is formed of materials whose density increases from the surface towards the centre. In support of the point, generally, sought to be established, namely, the greater specific gravity of the older rocks, I offer, first of all, the following clause from the twentythird Theorem:-" That they (geologists) also concur in considering the primary rocks, besides being deficient in inorganic remains, to be more compact and crystalline in texture than the others." The following are some of the authorities for that opinion: "When we trace," says Dr. Fleming, "the characters of the different depositions which have taken place, from the newest alluvial beds to the oldest transition rocks, we witness very remarkable gradations of character. The newest-formed strata are loose in their texture, and usually horizontal in their position. In proportion as we retire from these towards the older formations, the texture becomes more compact and crystalline, and the strata become more inclined. These characters may be traced by comparing the common loose marl of a peat-bog with the former chalk; the compact floetz limestone with the transition marble; or the peat itself with the older beds of wood coal, or the still older beds of coal of the independent coal |
