Whatever exhibited an aspect in any degree extraordinary was sure to attract the notice of the old Highlanders,—an acutely observant race, however slightly developed their reflective powers; and the great natural objects which excited their attention we always find associated with some traditionary story. It is said that in the Conglomerate cliffs above Brahan, a retainer of the Mackenzie, one of the smiths of the tribe, discovered a rich vein of silver, which he wrought by stealth, until he had filled one of the apartments of his cottage with bars and ingots. But the treasure, it is added, was betrayed by his own unfortunate vanity, to his chief, who hanged him in order to serve himself his heir; and no one since his death has proved ingenious enough to convert the rude rock into silver. Years had, I found, wrought their changes amid the miniature Highlands of the Conglomerate. The sapplings of the straggling wood on the banks of Loch Ousy,—the pleasant little lake, or lochan rather, of this upland region,—that I remembered having seen scarce taller than myself, had shot into vigorous treehood; and the steep slopes of Knock Farril, which I had left covered with their dark screen of pine, were now thickly mottled over with half-decayed stumps, and bore that peculiarly barren aspect which tracts cleared of their wood so frequently assume in their transition state, when the plants that flourished in the shade have died out in consequence of the exposure, and plants that love the open air and the unbroken sunshine have not yet sprung up in their place. I found the southern acclivities of the hill covered with scattered masses of vitrified stone, that had fallen from the fortalice atop; and would recommend to the collector in quest of a characteristic specimen, that instead of laboring, to the general detriment of the pile, in detaching one from the walls above, he should set himself to seek one here. The blocks, uninjured by the hammer, exhibit, in most cases, the angular character of the original fragments better than those forcibly detached from the mass, and preserve in fine keeping those hollower interstices which were but partially filled with the molten matter, and which, when shattered by a blow, break through and lose their character.
One may spend an hour very agreeably on the green summit of Knock Farril. And at almost all seasons of the year a green summit it is,—greener considerably than any other hill-top in this part of the country. The more succulent grasses spring up rich and strong within the walls, here and there roughened by tufts of nettles, tall and rank, and somewhat perilous of approach,—witnesses, say the botanists, that man had once a dwelling in the immediate neighborhood. The green luxuriance which characterizes so many of the more ancient fortalices of Scotland seems satisfactorily accounted for by Dr. Fleming, in his "Zoölogy of the Bass." "The summits and sides of those hills which were occupied by our ancestors as hill-forts," says the naturalist, "usually exhibit a far richer herbage than corresponding heights in the neighborhood with the mineral soil derived from the same source. It is to be kept in view, that these positions of strength were at the same time occupied as hill-folds, into which, during the threatened or actual invasion of the district by a hostile tribe, the cattle were driven, especially during the night, as to places of safety, and sent out to pasture in the neighborhood during the day. And the droppings of these collected herds would, as takes place in analogous cases at present, speedily improve the soil to such an extent as to induce a permanent fertility." The further instance adduced by the Doctor, in showing through what protracted periods causes transitory in themselves may remain palpably influential in their effects, is curiously suggestive of the old metaphysical idea, that as every effect has its cause, "recurring from cause to cause up to the abyss of eternity, so every cause has also its effects, linked forward in succession to the end of time." On the bleak moor of Culloden the graves of the slain still exist as patches of green sward, surrounded by a brown groundwork of stunted heather. The animal matter,—once the nerves, muscles, and sinews of brave men,—which originated the change, must have been wholly dissipated ages ago. But the effect once produced has so decidedly maintained itself, that it remains not less distinctly stamped upon the heath in the present day than it could have been in the middle of the last century, only a few years after the battle had been stricken.
The vitrification of the rampart which on every side incloses the grassy area has been more variously, but less satisfactorily, accounted for than the green luxuriance within. It was held by Pennant to be an effect of volcanic fire, and that the walls of this and all our other vitrified strongholds are simply the crater-rims of extinct volcanoes,—a hypothesis wholly as untenable in reference to the hill-forts as to the lime-kilns of the country: the vitrified forts are as little volcanic as the vitrified kilns. Williams, the author of the "Mineral Kingdom," and one of our earlier British geologists, after deciding, on data which his peculiar pursuits enabled him to collect and weigh, that they are not volcanic, broached the theory, still prevalent, as their name testifies, that they are artificial structures, in which vitrescency was designedly induced, in order to cement into solid masses accumulations of loose materials. Lord Woodhouselee advocated an opposite view. Resting on the fact that the vitrification is but of partial occurrence, be held that it had been produced, not of design by the builders of the forts, but in the process of their demolition by a besieging enemy, who, finding, as he premised, a large portion of the ramparts composed of wood, had succeeded in setting them on fire. This hypothesis, however, seems quite as untenable as that of Pennant. Fires not unfrequently occur in cities, among crowded groups of houses, where walls of stone are surrounded by a much greater profusion of dry woodwork than could possibly have entered into the composition of the ramparts of a hill-fort; but who ever saw, after a city fire, masses of wall from eight to ten feet in thickness fused throughout? The sandstone columns of the aisles of the Old Greyfriars in Edinburgh, surrounded by the woodwork of the galleries, the flooring, the seating, and the roof, were wasted, during the fire which destroyed the pile, into mere skeletons of their former selves; but though originally not more than three feet in diameter, they exhibited no marks of vitrescency. And it does not seem in the least probable that the stonework of the Knock Farril rampart could, if surrounded by wood at all, have been surrounded by an amount equally great, in proportion to its mass, as that which enveloped the aisle-columns of the Old Greyfriars.
The late Sir George Mackenzie of Coul adopted yet a fourth view. He held that the vitrification is simply an effect of the ancient beacon-fires kindled to warn the country of an invading enemy. But how account, on this hypothesis, for ramparts continuous, as in the case of Knock Farril, all round the hill? A powerful fire long kept up might well fuse a heap of loose stones into a solid mass; the bonfire lighted on the summit of Arthur Seat in 1842, to welcome the Queen on her first visit to Scotland, particularly fused numerous detached fragments of basalt, and imparted, in some spots to the depth of about half an inch, a vesicular structure to the solid rock beneath. But no fire, however powerful, could have constructed a rampart running without break for several hundred feet round an insulated hill-top. "To be satisfied," said Sir George, "of the reason why the signal-fires should be kindled on or beside a heap of stones, we have only to imagine a gale of wind to have arisen when a fire was kindled on the bare ground. The fuel would be blown about and dispersed, to the great annoyance of those who attended. The plan for obviating the inconvenience thus occasioned which would occur most naturally and readily would be to raise a heap of stones, on either side of which the fire might be placed to windward; and to account for the vitrification appearing all round the area, it is only necessary to allow the inhabitants of the country to have had a system of signals. A fire at one end might denote something different from a fire at the other, or in some intermediate part. On some occasions two or more fires might be necessary, and sometimes a fire along the whole line. It cannot be doubted," he adds, "that the rampart was originally formed with as much regularity as the nature of the materials would allow, both in order to render it more durable, and to make it serve the purposes of defence." This, I am afraid, is still very unsatisfactory. A fire lighted along the entire line of a wall inclosing nearly an acre of area could not be other than a very attenuated, wire-drawn line of fire indeed, and could never possess strength enough to melt the ponderous mass of rampart beneath, as if it had been formed of wax or resin. A thousand loads of wood piled in a ring round the summit of Knock Farril, and set at once into a blaze, would wholly fail to affect the broad rampart below; and long ere even a thousand, or half a thousand, loads could have been cut down, collected, and fired, an invading enemy would have found time enough to moor his fleet and land his forces, and possess himself of the lower country. Again, the unbroken continuity of the vitrified line militates against the signal-system theory. Fire trod so closely upon the heels of fire, that the vitrescency induced by the one fire impinged on and mingled with the vitrescency induced by the others beside it. There is no other mode of accounting for the continuity of the fusion; and how could definite meanings possibly be attached to the various parts of a line so minutely graduated, that the centre of the fire kindled on any one graduation could be scarce ten feet apart from the centre of the fire kindled on any of its two neighboring graduations? Even by day, the exact compartment which a fire occupied could not be distinguished, at the distance of half a mile, from its neighboring compartments, and not at all by night, at any distance, from even the compartments farthest removed from it. Who, for instance, at the distance of a dozen miles or so, could tell whether the flame that shone out in the darkness, when all other objects around it were invisible, was kindled on the east or west end of an eminence little more than a hundred yards in length? Nay, who could determine,—for such is the requirement of the hypothesis,—whether it rose from a compartment of the summit a hundred feet distant from its west or east end, or from a compartment merely ninety or a hundred and ten feet distant from it? The supposed signal system, added to the mere beacon hypothesis, is palpably untenable.
The theory of Williams, however, which is, I am inclined to think, the true one in the main, seems capable of being considerably modified and improved by the hypothesis of Sir George. The hill-fort,—palpably the most primitive form of fortalice or stronghold originated in a mountainous country,—seems to constitute man's first essay towards neutralizing, by the art of fortification, the advantages of superior force on the side of an assailing enemy. It was found, on the discovery of New Zealand, that the savage inhabitants had already learned to erect exactly such hill-forts amid the fastnesses of that country as those which were erected two thousand years earlier by the Scottish aborigines amid the fastnesses of our own. Nothing seems more probable, therefore, than that the forts of eminences such as Craig Phadrig and Knock Farril, originally mere inclosures of loose, uncemented stones, may belong to a period not less ancient than that of the first barbarous wars of Scotland, when, though tribe battled with tribe in fierce warfare, like the red men of the West with their brethren ere the European had landed on their shores, navigation was yet in so immature a state in Northern Europe as to secure to them an exemption from foreign invasion. In an after age, however, when the roving Vikings had become formidable, many of the eminences originally selected, from their inaccessibility, as sites for hill-forts, would come to be chosen, from their prominence in the landscape, as stations for beacon-fires. And of course the previously erected ramparts, higher always than the inclosed areas, would furnish on such hills the conspicuous points from which the fires could be best seen. Let us suppose, then, that the rampart-crested eminence of Knock Farril, seen on every side for many miles, has become in the age of northern invasion one of the beacon-posts of the district, and that large fires, abundantly supplied with fuel by the woods of a forest-covered country, and blown at times into intense heat by the strong winds so frequent in that upper stratum of air into which the summit penetrates, have been kindled some six or eight times on some prominent point of the rampart, raised, mayhap, many centuries before. At first the heat has failed to tell on the stubborn quartz and feldspar which forms the preponderating material of the gneisses, granites, quartz rocks, and coarse conglomerate sandstones on which it has been brought to operate; but each fire throws down into the interstices a considerable amount of the fixed salt of the wood, till at length the heap has become charged with a strong flux; and then one powerful fire more, fanned to a white heat by a keen, dry breeze, reduces the whole into a semi-fluid mass. The same effects have been produced on the materials of the rampart by the beacon-fires and the alkali, that were produced, according to Pliny, by the fires and the soda of the Phœnician merchants storm-bound on the sands of the river Belus. But the state of civilization in Scotland at the time is not such as to permit of the discovery being followed up by similar results. The semi-savage guardians of the beacon wonder at the accident, as they well may; but those happy accidents in which the higher order of discoveries originate occur in only the ages of cultivated minds; and so they do not acquire from it the art of manufacturing glass. It could not fail being perceived, however, by intellects at all human, that the consolidation which the fires of one week, or month, or year, as the case happened, had effected on one portion of the wall, might be produced by the fires of another week, or month, or year, on another portion of it; that, in short, a loose incoherent rampart, easy of demolition, might be converted, through the newly-discovered process, into a rampart as solid and indestructible as the rock on which it rested. And so, in course of time, simply by shifting the beacon-fires, and bringing them to bear in succession on every part of the wall, Knock Farril, with many a similar eminence in the country, comes to exhibit its completely vitrified fort where there had been but a loosely-piled hill-fort before. It in no degree militates against this compound theory,—borrowed in part from Williams and in part from Sir George,—that there are detached vitrified masses to be found on eminences evidently never occupied by hill-forts; or that there are hill-forts on other eminences only partially fused, or hill-forts on many of the less commanding sites that bear about them no marks of fire at all. Nothing can be more probable than that in the first class of cases we have eminences that had been selected as beacon-stations, which had not previously been occupied by hill-forts; and in the last, eminences that had been occupied by hill-forts which, from their want of prominence in the general landscape, had not been selected as beacon-stations. And in the intermediate class of cases we have probably ramparts that were only partially vitrified, because some want of fuel in the neighborhood had starved the customary fires, or because fires had to be less frequently kindled upon them than on the more important stations; or, finally, because these hill-forts, from some disadvantage of situation, were no longer used as places of strength, and so the beacon-keepers had no motive to attempt consolidating them throughout by the piecemeal application of the vitrifying agent. But the old Highland mode of accounting for the present appearance of Knock Farril and its vitrified remains is perhaps, after all, quite as good in its way as any of the modes suggested by the philosophers.[20]
I spent some time, agreeably enough, beside the rude rampart of Knock Farril, in marking the various appearances exhibited by the fused and semi-fused materials of which it is composed,—the granites, gneisses, mica-schists, hornblendes, clay-slates, and red sandstones of the locality. One piece of rock, containing much lime, I found resolved into a yellow opaque substance, not unlike the coarse earthenware used in the making of ginger-beer bottles; but though it had been so completely molten that it had dropped into a hollow beneath in long viscid trails, it did not contain a single air-vesicle; while another specimen, apparently a piece of fused mica-schist, was so filled with air-cells, that the dividing partitions were scarcely the tenth of a line in thickness. I found bits of schistose gneiss resolved into green glass; the Old Red Sandstone basis of the Conglomerate, which forms the hill, into a semi-metallic scoria, like that of an iron-smelter's furnace; mica into a gray, waxy-looking stone, that scratched glass; and pure white quartz into porcellanic trails of white, that ran in one instance along the face of a darker-colored rock below, like streaks of cream along the sides of a burnt china jug. In one mass of pale large-grained granite I found that the feldspar, though it had acquired a vitreous gloss on the surface, still retained its peculiar rhomboidal cleavage; while the less stubborn quartz around it had become scarce less vesicular and light than a piece of pumice. On some of the other masses there was impressed, as if by a seal, the stamp of pieces of charcoal; and so sharply was the impression retained, that I could detect on the vitreous surface the mark of the yearly growths, and even of the medullary rays, of the wood. In breaking open some of the others, I detected fragments of the charcoal itself, which, hermetically locked up in the rock, had retained all its original carbon. These last reminded me of specimens not unfrequent among the trap-rocks of the Carboniferous and Oölitic systems. From an intrusive overlying wacke in the neighborhood of Linlithgow I have derived for my collection pieces of carbonized wood in so complete a state of keeping, that under the microscope they exhibit unbroken all the characteristic reticulations of the coniferæ of the Coal Measures.
I descended the hill, and, after joining my friends at Strathpeffer,—Buchubai Hormazdji among the rest,—visited the Spa, in the company of my old friend the minister of Alness. The thorough identity of the powerful effluvium that fills the pump-room with that of a muddy sea-bottom laid bare in warm weather by the tide, is to the dweller on the sea-coast very striking. It is identity,—not mere resemblance. In most cases the organic substances undergo great changes in the bowels of the earth. The animal matter of the Caithness ichthyolites exists, for instance, as a hard, black, insoluble bitumen, which I have used oftener than once as sealing-wax; the vegetable mould of the Coal Measures has been converted into a fire-clay, so altered in the organic pabulum, animal and vegetable, whence it derived its fertility, that, even when laid open for years to the meliorating effects of the weather and the visits of the winged seeds, it will not be found bearing a single spike or leaf of green. But here, in smell, at least, that ancient mud, swum over by the Diplopterus and the Diplacanthus, and in which the Coccosteus and Pterichthys burrowed, has undergone no change. The soft ooze has become solid rock, but its odoriferous qualities have remained unaltered. I next visited an excavation a few hundred yards on the upper side of the pump-room, in which the gray fetid breccia of the Strath has been quarried for dyke-building, and examined the rock with some degree of care, without, however, detecting in it a single plate or scale. Lying over that Conglomerate member of the system which, rising high in the Knock Farril range, forms the southern boundary of the valley, it occupies the place of the lower ichthyolitic bed, so rich in organisms in various other parts of the country; but here the bed, after it had been deposited in thin horizontal laminæ, and had hardened into stone, seems to have been broken up, by some violent movement, into minute sharp-edged fragments, that, without wear or attrition, were again consolidated into the breccia which it now forms. And its ichthyolites, if not previously absorbed, were probably destroyed in the convulsion. Detached scales and spines, however, if carefully sought for in the various openings of the valley, might still be found in the original laminæ of the fragments. They must have been amazingly abundant in it once; for so largely saturated is the rock with the organic matter into which they have been resolved, that, when struck by the hammer, the impalpable dust set loose sensibly affects the organs of taste, and appeals very strongly to those of smell. It is through this saturated rock that the mineral springs take their course. Even the surface-waters of the valley, as they pass over it contract in a perceptible degree its peculiar taste and odor. With a little more time to spare, I would fain have made this breccia of the Old Red the subject of a few simple experiments. I would have ground it into powder, and tried upon it the effect both of cold and hot infusion. Portions of the water are sometimes carried in casks and bottles, for the use of invalids, to a considerable distance; but it is quite possible that a little of the rock, to which the water owes its qualities, might, when treated in this way, have all the effects of a considerable quantity of the spring. It might be of some interest, too, to ascertain its qualities when crushed, as a soil, or its effect on other soils; whether, for instance, like the old sterile soils of the Carboniferous period, it has lost, through its rock-change, the fertilizing properties which it once possessed; or whether it still retains them, like some of the coprolitic beds of the Oölite and Greensand, and might not, in consequence, be employed as a manure. A course of such experiments could scarce fail to furnish with agreeable occupation some of the numerous annual visitants of the Spa, who have to linger long, with but little to engage them, waiting for what, if it once fairly leave a man, returns slowly, when it returns at all.
In mentioning at the dinner-table of my friend my scheme of infusing rock in order to produce Spa water, I referred to the circumstance that the Belemnite of our Liasic deposits, when ground into powder, imparts to boiling water a peculiar taste and smell, and that the infusion, taken in very small quantities, sensibly affects both palate and stomach. And I suggested that Belemnite water, deemed sovereign of old, when the Belemnite was regarded as a thunderbolt, in the cure of bewitched cattle, might be in reality medicinal, and that the ancient superstition might thus embody, as ancient superstitions not unfrequently do, a nucleus of fact. The charm, I said, might amount to no more than simply the administration of a medicine to sick cattle, that did harm in no case, and good at times. The lively comment of one of the young ladies on the remark amused us all. If an infusion of stone had cured, in the last age, cattle that were bewitched, the Strathpeffer water, she argued, which was, it seems, but an infusion of stone, might cure cattle that were sick now; and so, though the biped patients of the Strath could scarce fail to decrease when they knew that its infused stone contained but the strainings of old mud, and the juices of dead unsalted fish, it was gratifying to think that the poor Spa might still continue to retain its patients, though of a lower order. The pump-room would be converted into a rustic, straw-thatched shed, to which long trains of sick cattle, affected by weak nerves and dyspepsia, would come streaming along the roads every morning and evening, to drink and gather strength.
The following morning was wet and lowering, and a flat ceiling of gray cloud stretched across the valley, from the summit of the Knock Farril ridge of hills on the one side, to the lower flanks of Ben-Wevis on the other. I had purposed ascending this latter mountain,—the giant of the north-eastern coast, and one of the loftiest of our second-class Scottish hills anywhere,—to ascertain the extreme upper line at which travelled boulders occur in this part of the country. But it was no morning for wading knee-deep through the trackless heather; and after waiting on, in the hope the weather might clear up, watching at a window the poorer invalids at the Spa, as they dragged themselves through the rain to the water, I lost patience, and sallied out, beplaided and umbrellaed, to see from the top of Knock Farril how the country looked in a fog. At first, however, I saw much fog, but little country; but as the day wore on, the flat mist-ceiling rose together, till it rested on but the distant hills, and the more prominent features of the landscape began to stand out amid the more general gray, like the stronger lines and masses in a half-finished drawing, boldly dashed off in the neutral tint of the artist. The portions of the prospect generically distinct are, notwithstanding its great extent and variety, but few; and the partial veil of haze, by glazing down its distracting multiplicity of minor points, served to bring them out all the more distinctly. There is, first stretching far in a southern and eastern direction along the landscape, the rectilinear ridge of the Black Isle,—not quite the sort of line a painter would introduce into a composition, but true to geologic character. More in the foreground, in the same direction, there spreads a troubled cockling sea of the Great Conglomerate. Turning to the north and west, the deep valley of Strathpeffer, with its expanse of rich level fields, and in the midst its old baronial castle, surrounded by coeval trees of vast bulk, lies so immediately at the foot of the eminence, that I could hear in the calm the rush of the little stream, swollen to thrice its usual bulk by the rains of the night. Beyond rose the thick-set Ben-Wevis,—a true gneiss mountain, with breadth enough of shoulders, and amplitude enough of base, to serve a mountain thrice as tall, but which, like all its cogeners of this ancient formation, was arrested in its second stage of growth, so that many of the slimmer granitic and porphyritic hills of the country look down upon it, as Agamemnon, according to Homer, looked down upon Ulysses.