Omphalos: An Attempt to Untie the Geological Knot. Gosse Philip Henry

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СКАЧАТЬ side, however, has deposed in a contrary sense: and, though he has said but little, some of those who have heard the cause attach such weight to his testimony, that they do not feel satisfied to let it be overborne. Counsel on the former side have, indeed, cross-examined the Witness, and dissected his testimony with much skill, and they contend that what he said has been misunderstood by the minority; and that, as his words may at least bear a sense which would not contradict those of the opposing witness, the clear, copious, and unvarying deposition previously made, ought to command the verdict of the Court.

      The minority are silenced, but not satisfied; they know not how to give up the Witness on whose veracity they have been wont to rely; but they are unable to answer the arguments brought against him.

      Counsel for the Brachy-chronology speaks. "We respectfully ask the Court for another hearing. Will our learned brother permit his witness briefly to recapitulate his testimony, and we will endeavour to examine it once more; for we think we shall be able to detect some flaw in it?" Rule granted.

      WITNESS FOR THE MACRO-CHRONOLOGY.

      The following, then, is the substance of what the witness deposes. He is not a living witness; his testimony, therefore, is not oral, but written – lithographed, in fact. It consists of a number of documents, which are couched in a language and character not to be understood without some previous study, but yet very capable of translation – very clear and unmistakeable. The following, I say, is a condensed summary of the leading points.

      If a curious person had watched the process of making the excavations that were preliminary to the boring of the Thames Tunnel, he would have observed that the labourers exposed successive layers of earth, differing much in colour, consistency, and general character. First, an accumulation of soil, consisting of decayed vegetable and animal matter, mingled with broken pottery, and other rubbish of man's production, was removed; then a layer of sand, gravel, and river mud; then a bed of reddish clay; then a layer of clay, mixed with silt or fine sandy mud; then a thin layer of silt, much filled with shells; then a stratum of stiff blue clay; then a layer of clay of more mottled character, containing a portion of silt, and some shells; then a stratum of very firm clay, so solid that it required to be broken with wedges; then a bed of gravel and sand of a green colour; and finally, a similar layer, but of a coarser texture.

      In the course of the hundred feet or so of perpendicular depth thus exposed, he would have seen a succession of layers, apparently deposited upon one another. But as yet he would have formed a very inadequate notion of the stratification of the earth's crust.

      With the knowledge thus gained, however, let him now make a little excursion into Hertfordshire; we will suppose at the time when the cuttings for the Great Northern Railway were being made. When he came near Cheshunt, he would see that the London clay, which he found underlying the Thames, crops out, or disappears by the stratum coming obliquely to the surface. He would see, however, another bed of clay – the plastic clay – beneath this, which now forms the superficial stratum, and continues to do so, till he gets beyond Hertford. There this stratum crops out; and the chalk, which for some time he has seen to underlie the plastic clay, now comes to the surface.

      Business or pleasure calls him to Bridlington on the Yorkshire coast; and he determines to make a pedestrian tour across the diameter of England to Whitehaven. He soon recognises the chalk, which constitutes the Wolds, and rises to about 800 feet above the sea level. Below its escarpment he traces the Kimmeridge clay, the uppermost of a series of strata more than 2,000 feet in thickness, that constitute the Oolitic system – including, among others, the coralline oolite, the calcareous grit, the cornbrash, thin, but rich in fossils; the lower sandstone and coal of the Cleveland hills, the alum shale, the marlstone, and the lower lias shale.

      Then comes a stratum of the saliferous system or the new red sandstone, with the red marls, perhaps not much short of a thousand feet deep. Below them the observer finds the strata of the magnesian limestone formation, for nearly 400 feet, resting on the great coal formations of vast depth. Of these the coal field of the West Riding is not less than 4,000 feet in depth, and beneath it lie the millstone grit, and the mountain limestone, 2,500 feet more, the latter displayed in noble grandeur on the faces of those wall-like precipices that inclose the romantic dales of the Swale and the Ure, and that subsequently tower in magnificent altitude on the sides of Pennygant and Ingleborough.

      On the western escarpment of the Pennine ridge, just as the traveller is entering Westmoreland, he would detect the bottom of the limestone; and here he would have an opportunity of seeing, what is rare in these parts, a stratum of the old red sandstone, lying between the former and the slaty rocks of the Cumbrian formations. And here at length, in the wild and magnificent scenery of these mountains, he sees the primitive and transition series, the greenstone, the sienite, and the granite, each of which is discernible in succession on the face of one or other of the lofty Fells of Cumberland.

      Our traveller now comes home, and, musing on what he has seen, counts up some thirty or more distinct strata lying in regular succession one on another. But he has not seen all the world, nor even all England; but he reads the results of many independent observations, and finds that while, for the most part, the strata which he has seen are common to the whole surface of the globe, and while the order of their superposition is invariable everywhere, others are in some parts added, while perhaps some of those which he has observed are locally absent. Thus he is able to form a more distinct idea of the stratification of the earth's crust as a whole. It is composed of about forty distinct formations, generally increasing in thickness as we go downwards, so that the whole cannot be much less than ten miles in depth, supposing them in any locality to be all present, and to be lying in the horizontal plane.

      Mathematicians have satisfactorily determined that the mean density of the globe is about five-and-a-half times that of water, or about twice that of granite, a fact inconsistent with any other supposition than that the interior is occupied by substances maintained in a fluid state by intense heat. The lowest point that has yet been patent to human observation is occupied by the granite, a compound rock, which bears evident marks of having been once in a state of fusion, and of having cooled slowly, and that under immense pressure, contracting and crystallizing as it parted with its heat. There is every reason to believe that the granite is not defined at its inferior surface, but that it merges into the molten mass, probably still solidifying.

      After the outer portion of the granite had cooled sufficiently to become solid, there is evidence that it was covered by water, agitated by powerful currents, and probably in a heated state. The action of these currents disintegrated the rock, and deposited the constituent substances at the bottom of the sea – on the surface, and in the hollows, of the granite. For there is reason to think that the contraction of the primitive rock in the process of cooling, produced irregular undulations or crumplings of the surface, and frequent fractures and dislocations, elevating some parts and depressing others. The gneiss, the mica-schist, and the clay-slate, which are found immediately overlying the granitic rock in strata of vast thickness, are but the components of granite, separated and rearranged. "If we imagine common granite coarsely pounded, and thrown into a vessel of water, it will arrange itself at the bottom of the vessel in a condition very much like that of gneiss, which is indeed nothing else than stratified granite. If the water in which the pounded rock is thrown is moving along at a slow rate, and the clayey portion of the granite, called felspar, happens to be somewhat decomposed, as it often is, then the felspar (which is so truly clay that it makes the best possible material for the use of the potteries) and the thin shining plates of mica, will be carried further by the water than the lumps of white quartz or flint sand, which, with the other two ingredients, made up the granite; and the two former will be deposited in layers, which, by passing a galvanic current through them, would in time become mica-schist. If the mica were absent, or if the clay were deposited without it, owing to any cause, then a similar galvanic current would turn the deposit into something like clay-slate."25

      The deposition of these strata, being formed out of granite, supposes СКАЧАТЬ