Diplopterus—new species.
CHAPTER X.
THE CARBONIFEROUS ROCKS—Continued.
The geology of the northern division of Scotland is, almost in every particular in the series of rocks that have been described, the counterpart of the southern, which now falls to be noticed. The fossils so richly imbedded in the former are here repeated, more sparingly in some, more abundantly in other families, and, in several instances, in the introduction of entirely new forms of organic life. Along the west and south border counties, the granites, with their associated crystalline group, are sparingly developed, stretching, at intervals, from the island of Arran through Galloway and Kirkcudbright into Dumfries-shire. The silurians follow in their order of superposition, occupying an extensive area from sea to sea across the island. The devonian system, chiefly in the upper and middle beds, wraps round the base of the older formation, and rests unconformably on its highly-inclined strata. The carboniferous deposits are widely distributed, some in isolated basins, and enveloped by the old red, and pregnant all of them with the fossils of the period. The ignigenous rocks, the traps and porphyries, are also very abundant, some in the form of detached cones, some in extensive ranges, and all demonstrative of their character as the agents that have lifted up, disrupted, and twisted the strata of the district.
In passing over this section of our course, it will not be necessary, therefore, to dwell in any minute or lengthened descriptions.
I. The geological student, in commencing his researches at Edinburgh, is immediately arrested by the more prominent objects that everywhere rise into view—the Castle Rock—the Calton Hill—Salisbury Crag—Arthur’s Seat—and the Pentlands. A wondrous, glorious scene, every one involuntarily exclaims, upon reaching any of these heights, thrown, as if by the hand of an enchanter, in and around this lovely city. Geology here has its favorite residence—the birth-place and cradle of the Huttonian Theory—Arthur’s seat there to attest its truth. What a history of bygone times recorded in these two words! What a revolution produced in the sentiments of mankind as to the science of world-making! And, still more, how deeply were men’s minds agitated, and the foundations of religious truth stirred, by the novel views which were then announced! The assumption lying at the foundation of the rival, or Wernerian theory, is, that the materials of which the various strata of the globe consist were originally dissolved or suspended in water: they were thus in a condition to assume any form which their physical qualities and the laws of matter might determine; and, accordingly, in this fluid menstruum they were consolidated into various combinations, partly by means of crystallization, and partly by mechanical deposition. The Huttonian theory, on the other hand, employs the force of subterraneous fire as its principal machinery, which is placed at immense depths, and the materials on which it operates are under a vast pressure; and, consequently, while they are indurated into limestone, sandstone, and coal, along with their included fossils, their essential qualities are but very slightly affected, and the arrangement and disposition of their particles but little disturbed. The hills around, by which this theory was to be tested, and to whose singular structure it owed its origin, consist of an alternating series of tabular masses of trap and the sedimentary deposits, basalt forming generally the central nucleus, with tufa, greenstone, and sandstone variously disposed and folded over. All the conditions of upheaval, tortion, angularity, induration, fracture, and dislocation, are amply furnished; the columnar, jointed structure is well defined in Samson’s Ribs; the very momentum of pressure, forcing the sandstone into the perpendicular, may be studied as a nice dynamical problem on the Castle rock; and when Sir James Hall brought from his crucible a reconstructed whinstone, regularly jointed and with no trace of vitreous fusion, the demonstration of the theory was felt and acknowledged, in its leading features, to be complete.
Palæontology has added its living wonders to the mere lithological speculations which were then in vogue and engrossed all attention. And geologists can now afford to smile at the misinterpretations, made by both parties, of established facts and well-ascertained things—nay, at the eagerness with which they irrelevantly pressed facts to bend to their conflicting views—the vehemence with which the Wernerian declared whinstone to contain organisms, and to be no exception to the law of mechanical deposition; while the Huttonian as deliberately set himself to prove that the nodules in chalk could only be the product of fire—the formation itself, as now determined, being merely a concretion of shells of the most perfect structure and undiminished luster. Truth, like light, emerges slowly, feeble in its dawnings when objects are obscurely seen or readily mistaken, a portion of the view half in shade, and half in brightness. And thus it has happened with both systems, as in the progress of the science errors have been detected and deficiencies supplied, peculiar to each. The acrimony of the contest, too, has passed away. Theology has been disentangled, and declared by the divine to be in no way affected by the issue. And while the scurrilities of the indiscreet abettors of both are utterly forgotten, the deductions of Hutton and the masterly expositions of his illustrator are in the main adopted as the basis of the only true system of geology.
II. In the general structure of the environs of the Scottish metropolis this plutonic machinery is deeply impressed, as it has been most vigorously exerted. There is everywhere the greatest derangement existing among the sedimentary deposits, everything is tossed out of its original place, and divided into small sections and detached groups. The connections and relative positions are very difficult to trace. Still, amidst all the disorder, the more general bearings of the different formations may be ascertained. Mr. Charles Maclaren, indeed, has examined everything with a pains-taking care, and described them with a minuteness and fidelity of detail, which cannot be surpassed, as they need scarcely be repeated. His “Geology of Fife and the Lothians,” will be in every student’s hands who desires to be acquainted with the structure of the district, conversant more especially as this learned geologist is with the position, fragments, and medal-stamp of every rock—their relations to each other, historical value, and bearings in the science—and illustrated with such diversity of section and diagram, that we feel as we accompany him,—
“Panditur interea domus Omnipotentis.”