Page images
PDF
EPUB

working that they might live. One of the three had fixed its crimson base on the white surface of a fossil coral; the pentagonal cavities, out of each of which a creature of resembling form had once stretched its slim body and still minuter petals, to agitate the water with similar currents, were lying open around it . In another corner of the pool a sea-urchin was slowly dragging himself up the slope, with all his red fleshy hawsers that could be brought to bear, and all his nearer handspokes hard strained in the work. His progress resembled that of the famous Russian boulder, transported for so many miles to make a pedestal for the statue of Peter the Great; with this difference, however, that here it was the boulder itself that was plying the handspokes and tightening the ropes. And lo! from the plane over which he moved there projected the remains of creatures of similar type;—the rock was strewed with fossil handspokes, greater in bulk than his, and somewhat diverse in form, but whose general identity of character it was impossible to mistake. The spines of echini, fretted with lines of projections somewhat in the style of the pinnacles of a Gothic building, lie as thickly in this deposit as in any deposit of the Chalk itself. The pool had its zoophytes of the arborescent form,—the rock its flustra; the pool had its cluster of minute muscles,—the rock its scallops and ostrea; the pool had its buccinidae,—the rock its numerous whorls of some nameless turreted shell; the pool had its cluster of serpulae,—the serpulae lay so thick in the rock, as to compose, in some layers, no inconsiderable proportion of its substance.

BRORA COAL-FIELD OTHER THAN THE TRUE COAL MEASURES.

A Coal-field in other than the true Coal Measures is always an object of peculiar interest to the geologist; and the coal-field of Brora is, in at least one respect, one of the most remarkable of these with which geologists are yet acquainted. The seams of the well-known Bovey coal of South Devon,—a lignite of the Tertiary,—are described as of greater depth; but it burns so imperfectly, and emits so offensive an odour, that, though used by some of the poorer cottagers in the neighbourhood, and some of the local potteries, it never became, nor can become, an article of commerce. It is curious merely as an immense accumulation of vegetable matter passing into the mineral state,—as, shall I venture to say, a sort of half-mineralized peat of the Tertiary,—a peat moss that, instead of overlying, underlies the diluvium. In the Brora coal, as might be inferred from its much greater age, the process of mineralization is more complete; and it furnishes, if I mistake not, the only instance in which a coal newer than that of the carboniferous era has been wrought for centuries, and made an article of trade. There were pits opened at Brora as early as the year 1598: they were re-opened at various intermediate periods in the seventeenth and eighteenth centuries; on one occasion, in the middle part of the latter, by Williams, the author of a Natural History of the Mineral Kingdom, which has been characterized by Lyell as 'a work of great merit for its day;' and during twelve years of the present century, from i8i4to 1826, there were extracted from but a single pit in this field no fewer than seventy thousand tons of coal. The Oolitic coal-field of Sutherland stands out in prominent relief amid the ligneous deposits that derive their origin from the later geological floras. And yet its commercial history does not serve to show that the speculations of the miner may be safely pursued in connexion with any other than that one wonderful flora which has done so much more for man, with its coal and its iron, than all the gold mines of the world. The Brora workings were at no time more than barely remunerative; and the fact that they were often opened to be as often abandoned, shows that they must have occasionally fallen somewhat below even this low line. Latterly, at least, it was rather the deficient quality of the coal that militated against the speculation, than any deficiency in the quantity found. It burned freely, and threw out a powerful flame; but it was accompanied by a peculiar odour, that seemed to tell rather of the vegetable of which it had been originally composed than of the mineral into which it had been converted, and then sunk into a white light ash, which every breath of air sent floating over carpets and furniture. And so, when brought into competition, in our northern ports, with the coal of the Mid-Lothian and English fields, it failed to take the market. The speculation of Williams was singularly unlucky. He became lessee ot the entire field about the year 1764, and wrought it for nearly five years. There occurs near the centre of the main seam a band of pyritiferous concretions, which here, as elsewhere, have the quality of taking fire spontaneously when exposed in heaps to air and moisture, and which his miners had not been sufficiently careful in excluding from the coal. A cargo which he had shipped from Portsoy, in Banffshire, took fire in this way, in consequence, it has been said, of the vessel springing a leak; and such was the alarm excited among his customers, that they declined dealing with him any longer for a commodity so dangerous. And so, after an ineffectual struggle, he had to relinquish his lease.

LONDON MUSEUM OF ECONOMIC GEOLOGY.

In the Museum of Economic Geology now in the course of forming in London, there are specimens exhibited of not only the various rude materials of art furnished by the mine and the quarry, but also of what these can be converted into by the chemist and the mechanic. Not only does it show the gifts of the mineral kingdom to man, but the uses also to which man has applied them. The rough and unpromising block of marble stands side by side with the exquisitely polished and delicately-sculptured vase. The bracelet of glittering steel, scarcely of less value than if wrought in gold, ranges in striking contrast with the earthy, umbry nodule of clay-ironstone. There are series of specimens, too, illustrative of the various changes which an earth or metal assumes in its progress through the workshop or the laboratory. Here, for instance, is the ironstone nodule,—there the roasted ore,—yonder the fused mass; the wrought bar succeeds; then comes the rudely-blocked ornament or implement; and, last Of all, the exquisitely finished piece of work, as we find it in the cutler's warehouse or the jeweller's shop.

I am not aware whether the museum also exhibits its sets of specimens illustrative of substances elaborated, not by man, but by nature herself, and elaborated, if one may so speak, on the principle of serial processes and succeeding stages. The arrangement in many cases would have to proceed, no doubt, on a basis of hypothesis; but the cases would also be many in which the hypothesis would at least not seem a forced one. It was suggested to me on the Brora coal-field, that the process through which nature makes coal might be strikingly illustrated in this style. One might almost venture to begin one's serial collection with a well-selected piece of fresh peat, containing its fragments of wood, its few blackened reeds, its fern-stalks, and its club-mosses. Another specimen of more solid and homogeneous structure, and darker hue, cut from the bottom of some deep morass, might be placed second in the series. Then might come a first specimen of Bovey coal, taken from under its eight or ten feet of Tertiary clay,—a specimen of light and friable texture, and that exhibited more of its original vegetable qualities than of its acquired mineral ones. A second specimen, brought from a deeper bed of the same deposit, might be chosen by the darker brown of its colour, and its nearer approximation to the structure of pit-coal. The Oolitic coal of the Brora or Yorkshire field might furnish at least two specimens more. And thus the collector might pass on, by easy gradations, to the true Coal Measures, and down through these to the deeply-seated anthracite of Ireland, or the still more deeply-seated anthracite of America,—not altogether so assured of his arrangement, perhaps, as in dealing with the processes of the laboratory or the workshop, but at least tolerably sure that both chemists and naturalists would find fewer reasons to challenge than to confirm it .

BRORA PEAT-MOSSES OF THE OOLITE.

The Brora field, so various in its deposits, must have existed in many various states,—now covered by salt water, now by fresh,—now underlying some sluggish estuary,— now presenting, perchance, a superaqueous surface, darkened by accumulations of vegetable matter,—and now, again, let down into the green depths of the sea. To realize such a change as the last, one has but to cross the Moray Firth at this point to the opposite land, and there see a peatmoss covered, during stream tides, by from two to three fathoms of water, and partially overlaid by a stratum of seasand, charged with its characteristic shells. It is a small coal-bed, kneaded out and laid by, though still in its state of extremest unripeness,—a coal-bed in the raw material; and there are not a few such on the coasts of both Great Britain and Ireland. Professor Fleming's description of the submerged forests of the Firths of Forth and Tay must be familiar to many of my readers. They must have heard, too, through the far-known Principles of Lyell, of the

« PreviousContinue »