Is it not interesting to find this very curious genus in both the lowest and highest fossiliferous beds of the system, and constituting, like the Trilobite genus of the Silurian group, its most characteristic organism? The Trilobite has a wide geological range, extending from the upper Cambrian rocks to the upper Coal Measures. But though the range of the genus is wide, that of every individual species of which it consists is very limited. The Trilobites of the upper Coal Measures differ from those of the Mountain Limestone; these again, with but one exception, from the Trilobites of the upper Silurian strata; these yet again from the Trilobites of the underlying middle beds; and these from the Trilobites that occur in the base of the system. Like the coins and medals of the antiquary, each represents its own limited period; and the whole taken together yield a consecutive record. But while we find them merely scattered over the later formations in which they occur, and that very sparingly, in the Silurian System we find them congregated in such vast crowds, that their remains enter largely into the composition of many of the rocks which compose it. The Trilobite is the distinguishing organism of the group, marrying, if I may so express myself, its upper and lower beds; and what the Trilobite is to the Silurian formations, the Pterichthys seems to be to the formations of the Old Red Sandstone; with this difference, that, so far as is yet known, it is restricted to this system alone, occurring in neither the Silurian System below, nor in the Coal Measures above.
I am but imperfectly acquainted with the localities in which the upper beds of the Old Red Sandstone underlie the lower beds of the Coal Measures, or where any gradation of character appears. The upper yellow sandstone belt is extensively developed in Moray, but it contains no trace of carbonaceous matter in even its higher strata, and no other remains than those of the Holoptychius and its contemporaries. The system in the north of Scotland differs as much from the carboniferous group in its upper as in its lower rocks; and a similar difference has been remarked in Fife, where the groups appear in contact a few miles to the west of St. Andrew's. In England, in repeated instances, the junction, as shown by Mr. Murchison, in singularly instructive sections, is well marked, the carboniferous limestones resting conformably on the Upper Old Red Sandstone. No other system interposed between them.
There is a Rabbinical tradition that the sons of Tubal-Cain, taught by a prophet of the coming deluge, and unwilling that their father's arts should be lost in it to posterity, erected two obelisks of brass, on which they inscribed a record of his discoveries, and that thus the learning of the family survived the cataclysm. The flood subsided, and the obelisks, sculptured from pinnacle to base, were found fast fixed in the rock. Now, the twin pyramids of the Old Red Sandstone, with their party-colored bars, and their thickly crowded inscriptions, belong to a period immensely more remote than that of the columns of the antediluvians, and they bear a more certain record. I have, perhaps, dwelt too long on their various compartments; but the Artist by whom they have been erected, and who has preserved in them so wonderful a chronicle of his earlier works, has willed surely that they should be read, and I have perused but a small portion of the whole. Years must pass ere the entire record can be deciphered; but, of all its curiously inscribed sentences, the result will prove the same—they will all be found to testify of the Infinite Mind.
[CHAPTER X.]
Speculations in the Old Red Sandstone, and their Character.—George, first Earl of Cromarty.—His Sagacity as a Naturalist at fault in one Instance.—Sets himself to dig for Coal in the Lower Old lied Sandstone.—Discovers a fine Artesian Well.—Value of Geological Knowledge in an economic View.—Scarce a Secondary Formation in the Kingdom in which Coal has not been sought for.—Mineral Springs of the Lower Old Red Sandstone.—Strathpeffer.—Its Peculiarities whence derived.—Chalybeate Springs of Easter Ross and the Black Isle.—Petrifying Springs.—Building-Stone and Lime of the Old Red Sandstone.—Its various Soils.
There has been much money lost, and a good deal won, in speculations connected with the Old Red Sandstone. The speculations in which money has been won have consorted, if I may so speak, with the character of the system, and those in which money has been lost have not. Instead, however, of producing a formal chapter on the economic uses to which its various deposits have been applied, or the unfortunate undertakings which an acquaintance with its geology would have prevented, I shall throw together, as they occur to me, a few simple facts illustrative of both.
George, first Earl of Cromarty, seems, like his namesake and contemporary, the too celebrated Sir George M'Kenzie, of Roseavoch, to have been a man of an eminently active and inquiring mind. He found leisure, in the course of a very busy life, to write several historical dissertations of great research, and a very elaborate Synopsis Apocalyptica. He is the author, too, of an exceedingly curious letter on the "Second Sight," addressed to the philosophic Boyle, which contains a large amount of amusing and extraordinary fact; and his description of the formation of a peat-moss in the central Highlands of Ross-shire has been quoted by almost every naturalist who, since the days of the sagacious, nobleman, has written on the formation of peat. His life was extended to extreme old age; and as his literary ardor remained undiminished till the last, some of his writings were produced at a period when most other men are sunk in the incurious indifferency and languor of old age. And among these later productions are his remarks on peat. He relates that, when a very young man, he had marked, in passing on a journey through the central Highlands of Ross-shire, a wood of very ancient trees, doddered and moss-grown, and evidently passing into a state of death through the last stages of decay. He had been led by business into the same district many years after, when in middle life, and found that the wood had entirely disappeared, and that the heathy hollow which it had covered was now occupied by a green, stagnant morass, unvaried in its tame and level extent by either bush or tree. In his old age he again visited the locality, and saw the green surface roughened with dingy-colored hollows, and several Highlanders engaged in it in cutting peat in a stratum several feet in depth. What he had once seen an aged forest had now become an extensive peat-moss.
Some time towards the close of the seventeenth century he purchased the lands of Cromarty, where his turn for minute observation seems to have anticipated—little, however, to his own profit—some of the later geological discoveries. There is a deep, wooded ravine in the neighborhood of the town, traversed by a small stream, which has laid bare, for the space of about forty yards in the opening of the hollow, the gray sandstone and stratified clays of the inferior fish bed. The locality is rather poor in ichthyolites, though I have found in it, after minute search, a few scales of the Osteolepis, and on one occasion one of the better marked plates of the Coccosteus; but in the vegetable impressions peculiar to the formation it is very abundant. These are invariably carbonaceous, and are not unfrequently associated with minute patches of bitumen, which, in the harder specimens, present a coal-like appearance; and the vegetable impressions and the bitumen seem to have misled the sagacious nobleman into the belief that coal might be found on his new property. He accordingly brought miners from the south, and set them to bore for coal in the gorge of the ravine. Though there was probably a register kept of the various strata through which they passed, it must have long since been lost; but from my acquaintance with this portion of the formation, as shown in the neighboring sections, where it lies uplifted against the granitic gneiss of the Sutors, I think I could pretty nearly restore it. They would first have had to pass for about thirty feet through the stratified clays and shales of the ichthyolite bed, with here and there a thin band of gray sandstone, and here and there a stratum of lime; they would next have had to penetrate through from eighty to a hundred feet of coarse red and yellow sandstone, the red greatly predominating. They would then have entered the great conglomerate, the lowest member of the formation; and in time, if they continued to urge their fruitless labors, they would arrive at the primary rock, with its belts of granite, and its veins and huge masses of hornblende. In short, there might be some possibility of their penetrating to the central fire, but none whatever of their ever reaching a vein of coal. From a curious circumstance, however, they were prevented from ascertaining, by actual experience, the utter barrenness of the formation.