It is difficult to arrange in the mind the geologic formations of Banffshire in their character as a series of deposits. The pages of the stony record which the county composes, like those of an unskilfully-folded pamphlet, have been strangely mixed together, so that page last succeeds in some places to page first, and, of the intermediate pages, some appear at the beginning of the work, and some at the end. It is not until we reach the western confines of the county, some two or three miles short of the river Spey, its terminal boundary in this direction, that we find the beds comparatively little disturbed, and arranged chronologically in their original places. In the eastern and southern parts of the shire, rocks widely separated by the date of their formation have been set down side by side in patches, occasionally of but inconsiderable extent. Now the traveller passes over a district of grauwacke, now over a re-formation of the Lias; anon he finds himself on a primary limestone,—gneiss, syenite, clay-slate, or quartz-rock; and yet anon amid the fossils of some outlier of the Old Red. The geological map of the county is, like Joseph's coat, of many colors. I remember seeing, when a boy, more years ago than I am inclined to specify, some workmen engaged in pulling down what had been a house-painter's shop, a full century before. The painter had been in the somewhat slovenly habit of cleaning his brushes by rubbing them against a hard-cast wall, which was covered, in consequence, by a many-colored layer of paint, a full half-inch in thickness, and as hard as a stone. Taking a little bit home with me, I polished it by rubbing the upper surface smooth; and, lo! a geological map. The strata of variously hued pigment, spread originally over the surface of the hard-cast wall, were cut open, by the denudation of the grindstone, into all manner of fantastic forms, and seemed thrown into all sorts of strange neighborhoods. The map lacked merely the additional perplexity of a few bold faults, with here and there a decided dike, in order to render it on a small scale a sort of miniature transcript of the geology of Banff; and I have very frequently found my thoughts reverting to it, in connection with deposits of this broken character. On a rough hard-cast basis of granite I have laid down in imagination, as if by way of priming, coat after coat of the primary rocks,—gneiss, and stratified hornblend, and mica-schist, and quartz-rock, and day-slate; and then, after breaking the coatings well up, and rubbing them well down, and so spoiling and crumpling up the work as to make their original order considerably a puzzle, I have begun anew to paint over the rough surface with thick coatings of grauwacke and grauwacke-slate. When this part of the operation was completed, I have again begun to break up and grind down,—here letting a tract of grauwacke sink into the broken primary,—there wearing it off the surface altogether,—yonder elevating the original granitic hard-cast till it rose over all the coatings, Primary and Palæozoic. And then I have begun to paint yet a third time with thick Old Red Sandstone pigment; and yet again to break up and wear down,—here to insert a tenon of the Old Red deep into a mortise of the grauwacke, as at Gamrie,—there to dovetail it into the clay-slate, as at Tomantoul,—yonder, after laying it across the upturned quartz-rock, as at Cullen, to rub by much the greater part of it away again, leaving but mere remainder-patches and fragments, to mark where it had been. Lastly, if I had none of the superior Palæozoic or Secondary formations to deal with, I have brushed over the whole, by way of finish, with the variously-derived coatings of the superficial deposits; and thus, as I have said, I have often completed, in idea, after the chance suggestion of the old painter's shop, my portable models of the geology of disturbed districts like the Banffshire one. The deposits of Moray are greatly less broken. Denudation has partially worn them down; but they seem to have almost wholly escaped the previous crumpling process.
CHAPTER IV.
Yellow-hued Houses Of Elgin—Geology of the Country indicated by the coloring of the Stone Houses—Fossils of Old Red north of the Grampians different from those of Old Red south—Geologic Formations at Linksfield difficult to be understood—Ganoid Scales of the Wealden—Sudden Reaction, from complex to simple, in the Scales of Fishes—Pore-covered Scales—Extraordinary amount of Design exhibited in Ancient Ganoid Scales—Holoptychius Scale illustrated by Cromwell's "fluted pot"—Patrick Duff's Geological Collection—Elgin Museum—Fishes of the Ganges—Armature of Ancient Fishes—Compensatory Defences—The Hermit-crab—Spines of the Pimelodi—Ride to Campbelton—Theories of the formation of Ardersier and Fortrose Promontories—Tradition of their construction by the Wizard, Michael Scott—A Region of Legendary Lore.
The prevailing yellow hue of the Elgin houses strikes the eye of the geologist who has travelled northwards from the Frith of Forth. He takes leave of a similar stone at Cupar-Fife,—a warmly-tinted yellow sandstone, peculiarly well-suited for giving effect to architectural ornament; and after passing along the deep-red sandstone houses of the shires of Angus and Kincardine, and the gneiss, granite, hyperstene, and mica-schist houses of Aberdeen and Banff shires, he again finds houses of a deep red on crossing the Spey, and houses of a warm yellow tint on reaching Elgin,—geologically the Cupar-Fife of the north. And the story that the colored buildings tell him is, that he has been passing, though by a somewhat circuitous route of a hundred and fifty miles, over an anticlinal geological section,—down in the scale till he reached Aberdeen and had gone a little beyond it, and then up again, until at Elgin he arrives at the same superior yellow bed of Old Red Sandstone which he had quitted at Cupar-Fife. Both beds contain the same organisms. The Holoptychius of Dura Den, near Cupar, must have sprung from the same original as the Holoptychius of the Hospital and Bishop-Mill quarries near Elgin; and it seems not improbable that the two beds, thus identical in their character and contents, may have existed, ere the upheaval of the Grampians broke their continuity, as an extended deposit, at the bottom of the same sea. But with this last and newest of the formations of the Old Red Sandstone the identity of the deposits to the south and north ceases. The strata which in the south overlie the yellow bed of the Holoptychius represent the Carboniferous period, the overlying strata in the north represent the Oölitic one. On the one side the miner sinks his shaft, and finds a true coal, composed of the Stigmaria, Calamites, Club-mosses, Ferns, and Araucarians of the Palæozoic era; he sinks his shaft on the other side, and finds but thin seams of an imperfect lignite, composed of the Cycadeæ, Pines, Sphenopteri, and Clathraria of the Secondary period. The flora which found its subsoil in the Old Red Sandstone north of the Grampians, belonged to a scene of things so much more modern than the flora which found its subsoil in the Old Red Sandstone of the south, that all its productions were green and flourishing, waving beside lake, river, and sea, at a time when the productions of the other were locked up, as now, in sand and shale, lime and clay,—the dead mummies of ages long departed.
Another thoroughly wet morning! varied only from the morning of the preceding day by the absence of wind, and the greater weight of the persevering vertical rain, that leaped upwards in myriads of little dancing pyramids from the surface of every pool. I walked out under cover of my umbrella, to renew my acquaintance with the outlier of the Weald at Linksfield, and ascertain what sort of section it now presented under the quarrying operations of the limeburners. There was, however, little to be seen; the bands of green and blue clays, alternating with strata of fossiliferous limestone, and layers of a gray shade, thickly charged with minute shells of Cypris, were sadly blurred this morning by the trail of numerous slips from above, which had fallen during the rains, and softened into mud as they rushed downwards athwart the face of the quarry: and the arched band of boulder-clay which so mysteriously underlies the deposit was, save in a few parts, wholly covered up by the debris. The occurrence of the clay here as an inferior bed, with but the cornstone of the Old Red beneath, and all the beds of the Weald resting over it, forms a riddle somewhat difficult of solution; but it is palpably not reading it aright to regard the deposit, with at least one geologist who has written on the subject, as older than the rocks above. It is, on the contrary, as a vast amount of various and unequivocal evidence demonstrates, incalculably more modern; nay, we find proof of the fact here in that very bed which has been instanced as rendering it doubtful; the clay of which the interpolation is composed is found to contain fragments, not only of the cornstone on which it rests, but also of the Wealden limestone and shales which it underlies. It forms the mere filling up of a flat-roofed cavern, or rather of two flat-roofed caverns,—for the limestone roof dipped in the centre to the cornstone floor,—which, previous to the times of the boulder-clay, had lain open in what was then, as now, an old-world deposit, charged with long extinct organisms, but which, during the iceberg period, was penetrated and occupied by the clay, as run lime penetrates and occupies the interstices of a dry-stone wall. It was no day for gathering fossils. I saw a few ganoid scales, washed by the rain from the investing rubbish, glittering on fragments of the limestone, with a few of the characteristic shells of the deposit, chiefly Unionidæ; but nothing worth bringing away. The adhesive clay of the Weald, widely scattered by the workmen, and wrought into mortar by the beating rains, made it a matter of some difficulty for the struggling foot to retain the shoe, and, sticking to my soles by pounds at a time, rendered me obnoxious to the old English nickname of "rough-footed Scot." And so, after traversing the heaps, somewhat like a fly in treacle, I had to yield to the rain above and the mud beneath, and to return to do in Elgin what cannot be done equally well in almost any other town of its size in Scotland,—pursue my geological inquiries under cover.
On this, as on other occasions, I was struck by the complex and very various forms assumed by the ganoid scales of the Wealden. Throughout the Oölitic system generally, including the Lias, there obtains a singular complexity of type in these little glittering tiles of enamelled bone, which contrasts strongly with the greatly more simple style which obtained among the ganoids of the Palæozoic period. In many of these last, as in the Cœlacanth family, including the genera Holoptychius, Asterolepis, and Glyptolepis, in all their many species, with at least one genus of Dipterians, the genus Dipterus, the external outline and arrangement of scale was as simple as in any of the Cycloid family of the present time. Like slates on a roof, each single scale covered two, and was covered by two in turn; and the only point of difference which existed in relation to the laying down of these massy slates of bone, and the laying down of the very thin ones of horn which cover fish such as the carp or salmon, was, that in the massier slates, the sides, or cover,—nicely bevelled, in order to preserve an equability of thickness throughout,—were so adjusted, that two scales at their edges, where they lay the one over the other, were not thicker than one scale at its centre. Even in the other ganoids, their contemporaries, such as the Osteolepis and Diplopterus, where the scales were ranged more in the tile fashion, side by side, there was, with much ingenious carpentry in the fitting, a general simplicity of form. It would almost appear, however, that ere the ganoid order reached the times of the Weald, the simple forms had been exhausted, and that nature, abhorring repetition, and ever stamping upon the scales some specific characteristic of the creature that bore them, was obliged to have recourse to forms of a more complex and involved outline. These latter-day scales send out nail-like spikes laterally and atop, to lay hold upon their neighbors, and exhibit in their undersides grooves that accommodated the nails sent out, in turn, by their neighbors, to lay hold upon them. Their forms, too, are indescribably various and fantastic. It seems curious enough, that immediately after this extremely artificial state of things, if I may so speak, the two prevailing orders of the fish of the present day, the Cycloids and Ctenoids, should have been ushered upon the scene, and more than the original simplicity of scale restored. There took place a sudden reäction, from the fantastic and the complex to the simple and the plain.
It is further worthy of notice, that though many of the ganoid scales of the Secondary systems, including those of the Wealden, glitter as brightly in burnished enamel as the more splendent scales of the Old Red Sandstone and Coal Measures, there is a curious peculiarity exhibited in the structure of many of the older scales of the highly enamelled class, which, so far as I have yet seen, does not extend beyond the Palæozoic period. The outer layer of the scale, which lies over a middle layer of a cellular cancellated structure, and corresponds, apparently, with that scarf-skin which in the human subject overlies the rete mucosum, is thickly set over with microscopic pores, funnel-shaped in the transverse section, and which, examined by a good glass, in the horizontal one resemble the puncturings of a sieve. The Megalichthys of the Coal Measures, with its various carboniferous congeners, with the genera Diplopterus, Dipterus, and Osteolepis of the Old Red Sandstone,—all brilliantly enamelled fish,—are thickly pore-covered. But whatever purpose these pores may have served, it seems in the Secondary period to have been otherwise accomplished, if, indeed, it continued to exist. It is a curious circumstance, that in no case do the pores seem to pass through the scale. Whatever their use, they existed merely as communications between the cells of the middle cancellated layer and the surface. In a fish of the Chalk,—Macropoma Mantelli,—the exposed fields of the scales are covered over with apparently hollow, elongated cylinders, as the little tubes in a shower-bath cover their round field of tin, save that they lie in a greatly flatter angle than the tubes; but I know not that, like the pores of the Dipterians and the Megalichthys, they communicated between the interior of the scale and its external surface. Their structure is at any rate palpably different, and they bear no such resemblance to the pores of the human skin as that which the Palæozoic pores present.
The amount of design exhibited in the scales of some of the more ancient ganoids,—design obvious enough to be clearly read,—is very extraordinary. A single scale of Holoptychius Nobilissimus,—fast locked up in its red sandstone rock,—laid by, as it were, for ever,—will be seen, if we but set ourselves to unravel its texture, to form such an instance of nice adaptation of means to an end as might of itself be sufficient to confound the atheist. Let me attempt placing one of these scales before the reader, in its character as a flat counter of bone, of a nearly circular form, an inch and a half in diameter, and an eighth-part of an inch in thickness; and then ask him to bethink himself of the various means by which he would impart to it the greatest possible degree of strength. The human skull consists of two tables of solid bone, an inner and an outer, with a spongy cellular substance interposed between them, termed the diploe; and such is the effect of this arrangement, that the blow which would fracture a continuous wall of bone has its force broken by the spongy intermediate layer, and merely injures the outer table, leaving not unfrequently the inner one, which more especially protects the brain, wholly unharmed. Now, such also was the arrangement in the scale of the Holoptychius Nobilissimus. It consisted of its two well-marked tables of solid bone, corresponding in their dermal character, the outer to the cuticle, the inner to the true skin, and the intermediate cellular layer to the rete mucosum; but bearing an unmistakable analogy also, as a mechanical contrivance, to the two plates and the diploe of the human skull. To the strengthening principle of the two tables, however, there were two other principles added. Cromwell, when commissioning for a new helmet, his old one being, as he expresses it, "ill set," ordered his friend to send him a "fluted pot," i.e., a helmet ridged and furrowed on the surface, and suited to break, by its protuberant lines, the force of a blow, so that the vibrations of the stroke would reach the body of the metal deadened and flat. Now, the outer table of the scale of the Holoptychius was a "fluted pot." The alternate ridges and furrows which ornamented its surface served a purpose exactly similar with that of the flutes and fillets of Cromwell's helmet. The inner table was strengthened on a different but not less effective principle. The human stomach consists of three coats; and two of these, the outermost or peritoneal coat, and the middle or muscular coat, are so arranged, that the fibres of the one cross at nearly right angles those of the other. The violence which would tear the compact sides of this important organ along the fibres of the outer coat, would be checked by the transverse arrangement of the fibres of the middle coat, and vice versa. We find the cotton manufacturer weaving some of his stronger fabrics on a similar plan;—they also are made to consist of two coats; and what is technically termed the tear of the upper is so disposed that it lies at an angle of forty-five degrees with the tear of the coat which lies underneath. Now, the inner table of the scale of the Holoptychius was composed, on this principle, of various layers or coats, arranged the one over the other, so that the fibres of each lay at right angles with the fibres of the others in immediate contact with it. In the inner table of one scale I reckon nine of these alternating, variously-disposed layers; so that any application of violence, which, in the language of the lath-splitter, would run lengthwise along the grain of four of them, would be checked by the cross grain in five. In other words, the line of the tear in five of the layers was ranged at right angles with the line of the tear in four. There were thus in a single scale, in order to secure the greatest possible amount of strength,—and who can say what other purposes may have been secured besides?—three distinct principles embodied,—the principle of the two tables and diploe of the human skull,—the principle of the variously arranged coats of the human stomach,—and the principle of Oliver Cromwell's "fluted pot." There have been elaborate treatises written on those ornate flooring-tiles of the classical and middle ages, that are occasionally dug up by the antiquary amid monastic ruins, or on the sites of old Roman stations. But did any of them ever tell a story half so instructive or so strange as that told by the incalculably more ancient ganoid tiles of the Palæozoic and Secondary periods?