John MacCulloch

“ I do not however mean to deny that instances exist where a real distinction of periods in trap rocks can be proved, and I have myself observed some which I shall perhaps have occasion to describe at a future opportunity. I am only desirous to enforce on geologists the necessity of drawing their distinctions from real and not from theoretical views, and of establishing criteria which are better founded, and which rest on more satisfactory evidence than that produced by the mere apparent or even real superposition of an unstratified above a stratified rock. ”

“ It will be seen that there are yet points unexplained, particularly respecting the trap rocks, a circumstance which will not surprise geologists who know that to patience, toil, and good seasons, must often be superadded good fortune; the casual discovery of perhaps the only point over a wide tract which is capable of yielding the explanation of which we are in pursuit.
As the mica slate and its associate the quartz rock are the most ancient of those which I have ascertained in Sky, I shall commence from them as the foundation of the whole structure. ”

“ Comparing from the summits of any of the hills the general aspect of the two groups, the spectator is inevitably struck with the different powers of resistance which the two classes of rock offer to the efforts of time, and looks forward perhaps to a distant day when the red hills shall be levelled with the land below, while the Cuchullin shall still lift its iron summit to the clouds. ”

“ Such are the difficulties which oppose the introduction of the most perfect marble which has yet been found in Britain, difficulties which, slight as they are, ought, together with the prevalence of established habits and of a commercial routine, to check the extravagant hopes which have been entertained in this country of superseding by its own produce the importation of foreign statuary marble. But it will not be rendering justice to the marble of Sky if I do not add, that it possesses a property not found in that of Carrara, and one of considerable importance, at least in small sculptures. ”

“ In the present corroded and tarnished state of the surfaces of these statues we cannot trace the nature or the defects of this variety, but an examination of its texture and composition in the broken fragments, serves to excite the deepest regret, that the genius of the greatest sculptor whom the world has seen, should for want of better materials have been condemned to bestow its energies on so perishable and so defective a stone. ”

“ It is not indeed till fragments of the rock are examined in the hand that the spectator can discover that he sees any thing but a bed of shale alternating with sandstone: but on thus examining the schist, it is found to be an extremely brittle and hard substance, of a black colour, giving fire freely with steel, sharp in the fragments, and with an obscurely rhomboidal fracture; this last character being the only one by which it can be distinguished from the fine grained basalts, particularly such as I have mentioned as occurring in the form of veins in the Cuchullin. ”

“ The stony district about the Kyle rich produces like the Cuchullin hills but a scanty covering of heath and grass, and is perhaps among the most unproductive of the island, since the decomposed quartz rock of which it consists, yields a soil even worse than the syenite of the Red hills, or the rocks of the Cuchullin group; yet on the sea shores a few fertile spots are found in cultivation.
The great northern division consists of one entire mass of trap, with the exception of a few narrow lines of limestone and sandstone to be found on some of the shores. ”

“ If the one set were proved to be constantly superior to one set of stratified rocks, and the other to a different and later set, the question of rank might be settled between them: but these connections are difficult to ascertain to a sufficient extent, and possibly none such exist. If one stratified rock is in one place superior to another, we are sure that it is every where superior; but if we have ever so clearly proved that a body of trap or of any other unstratified rock is superior and in contact in one place to any given stratum, we have no certainty that it is equally so every where. ”

“ The trap which I have mentioned is remarkable for the enormous quantity of zeolites imbedded in it, the mineralogical details of which I shall have occasion to speak more largely of hereafter. In the decomposed soils these are frequently found resisting change long after the rock is rotten and reduced to clay. But in many other cases they also are decomposed together with the soil, and in such quantity as to communicate their white colour to it, and with that colour doubtless a degree of additional fertility derived from the quantity of calcareous earth which they contain. ”

“ Neither air, light, nor water can make their way through this dense covering of a substance so notoriously impervious that it has been found of equal use with clay in puddling the artificial banks of canals. It forms in fact an adventitious and useless soil so entire and so impenetrable that it would be of equally little consequence to the land-owner in its present state, whether it where bedded on a rock of solid quartz or on the most fertile garden mould. ”

“ In the district of Sky which I am new considering, there appears, as far as an accurate mineralogical investigation can determine such a point without the aid of analysis, a considerable similarity of composition in the trap throughout the greatest part of the whole tract. In almost every place where the rock approaches the surface, it is found on cutting into it to be rotten to a considerable depth, often reduced superficially to an absolute soil, and although appearing below like a solid rock, capable of being cut without difficulty by the axe or spade. ”

“ There is a second set of veins however, which traverse not only the mountain trap but the veins first named, and which are clearly of a posterior date. These are much smaller, often indeed not exceeding half an inch in breadth, and are composed of an extremely fine and hard black basalt. They are less abundant than the first where even they exist, and they are not found in nearly so many situations. They are to be observed pretty frequently passing through the rock at Coruisk, and through the greenstone and clinkstone of Garsven, in the neighbourhood of which latter they abound. ”

“ It may be an interesting matter of speculation to inquire by what power the vicinity of trap operates in influencing the change from shale to Lydian stone, as well as in producing the much better known changes which occur in sandstone bordering on trap. If basalts have been in any case produced by the fusion of beds of slate, the necessary analogy between the Lydian stone and basalt will appear conspicuous, and we have only to consider it as a shale brought into the state of basalt by fusion, without such further disturbance as to destroy its original stratification. ”

“ I know not that any thing worthy of notice exists at the junction. All the strata, both of schist and sandstone, are here as equal and straight as elsewhere, or if they are disturbed it is by the trap veins which are independent of the mountain. Nor are these rocks marked by any particular induration or affection of their composition. Yet I may remark that their angular elevation is less regular than at Loch Eishort, and that they are frequently inclined at much higher angles with the horizon than in this latter place. ”

“ It is well known that the permanence of trap veins is sometimes less, sometimes greater than that of the surrounding rocks. Hence they sometimes project like walls, while at others their ruin produces fissures or caves. This latter effect has taken place here, marking a great tendency to decomposition in these veins, since the including rocks do not seem to be of a very durable nature. The depth to which they have been excavated is often very considerable: in the case, of the spar cave including the external fissure, it cannot be less than 250 feet. ”

“ The purity of its colour is seldom contaminated; its fracture is granular and splintery, and its texture fine, less fine than that of Iona, but more so than that of Assynt: its compactness, hardness, and gravity, are greater than those of the marble of Carrara, which it in fact resembles in little else than colour. It is apparently well fitted for all purposes of sculpture, as it can be wrought in any direction, and has sufficient transparency, while at the same time it assumes even a better polish than is required for statuary. ”

“ Few substances in the catalogue of those with which economical mineralogy is concerned have excited more interest than statuary marble, from its rarity, its beauty, and its indispensable necessity in the art of sculpture. It has at different times formed an object of anxious research in this country, and premiums have been held out for it by the Society of Arts. It has consequently been found in various parts of Scotland, as well as in Ireland, but no native specimens have yet been introduced into the arts. ”

“ This is far from being the only case in nature where mere mineral distinctions are insufficient to determine the geological situation of a rock. In the stratified classes of rocks, both primary and secondary, these resemblances are frequent, since it is often impossible to distinguish quartz rock from sandstone, the breccias which it contains from the more recent graywacké, ancient clay slate from recent, or, as I have shown in this very account of Sky, primitive from secondary limestones. ”

“ At the bottom of this bay they descend suddenly into the sea, brown and bare, with scarcely a spot of verdure to enliven their dark sides, the only semblance of life they possess consisting in the motion of the few cascades which foam down their rugged declivities. ”

“ Similarly fertile soils are found in the vallies on its western side, while the central division, formed of syenite or quartz rock, produces the usual covering of those rocks, heath. In Strathaird, nearly the whole peninsula of which consists of secondary strata, we find a soil as fertile as we should expect on such a basis and in such a climate; a soil however owing less to art than to nature, whose bountiful efforts are seldom much assisted by highland industry or knowledge. ”

“ It is here so common, occupying cavities of greater or less magnitude, that a fourth or fifth part of the total bulk of the rock is sometime constituted by the chabasite. As far as I have observed, the chabasite which I have described is never, like the analcime, imbedded in the filamentous mesotype, but is not unfrequently associated in the same cavity both with stilbite and with analcime, nor is it unusual to find minute and well formed crystals of this latter substance, imbedded in the crystal of chabasite. ”

“ It is by no means regularly stratified, nor is it possible to trace for any considerable distance even the fragments of a regular prolongation of the edges of beds, such as is so distinctly exhibited in the quartz rock of Jura; yet there are evident marks of stratification, which in many places are sufficiently regular and extensive to justify the belief that it has once possessed a greater degree of regularity and extent, which have been disturbed by subsequent changes. ”

“ This rock seems indeed absolutely inimical to vegetation, nor does it appear to undergo the slightest decomposition, or to admit of the formation of soil, the detached fragments showing as little tendency to waste as the mountain itself. Had the globe of the earth been entirely formed of this rock it would still have been lifeless and void. It was among these fragments that I observed a rocking stone of considerable size and easily moved, having to all appearance fallen on such an edge as to allow of the conditions required for producing this effect. ”

“ Although the elevation of the country is considerable, and the climate among the most rainy of this kingdom, Sky affords no rivers of magnitude: their course is too short to admit of the accumulation of large streams. The river which runs into loch Sligachan carries more water to the sea than any other, and after it perhaps follow in order those which run into the lochs Harpart, Slapin, Eishort, Bracadale, Portree, Snizort, and Broadford. ”

“ I have here, as on other occasions, applied to these veins the general term trap, for the same reasons which I assigned in speaking of the rocks of this class, namely, that they vary in composition, although basalt is certainly the prevalent substance in them here and every where else. The order which I have allotted for them in this description is also the order which they hold in nature, since they traverse every rock that lies in their way from the most ancient to the most recent, seldom suffering any change either of direction or composition in this varying course. ”

“ Similar caves are of frequent occurrence between Talisker and Loch Brittle, the low projecting rocks being also often perforated by arches which are sometimes exceedingly complicated and remarkable. With the exception of some, projecting points of high rock the shores of Loch Bracadale are flat, and this tract is among the most fertile of Sky. At its southern extremity the cliffs are perfectly vertical, and without that slope at the foot, which so commonly accompanies the high cliffs of trap, and which are so conspicuous in particular on the eastern side of the island. ”

“ Its shores are every where covered with huge fragments of rock detached from the mountains above, and it contains two or three small islands which diversify in some measure the darkness of its surface. The nakedness of the rocks is not poetical. On the declivity of the mountain Garsven in particular, they rise from the base to the very summit, a height of at least 3000 feet, in huge smooth sheets at a very high angle, perfectly bare and of a dark iron brown colour, not chequered even by the growth of a single lichen or by one foreign tint to enliven the uniform gloom of the surface. ”

“ It is perhaps superfluous to say that nodules of chalcedony, often hollow and containing crystallized quartz, are occasionally found in the trap rocks of Sky, since they are of such common occurrence in this substance. The cavities are sometimes, in addition, sprinkled with crystals of stilbite, of analcime, and of chabasite.
Of those mineral substances which are the least frequent in trap rocks, steatite occurs in considerable quantity; it is tender, and always of a greenish dirty hue. It is sometimes found in very small nodules ”

“ The whole tract is however but little interesting, since the uniformity of this rock is only varied by the occasional occurrence of veins of trap and of quartz. If I could determine that the beds of mica slate had a regular position, I would say that they were succeeded by quartz rock, and that this rock terminated near Loch Eishort, being followed by a succession of rocks to be described immediately; but to determine such a succession, a regular disposition is indispensable, since, without that, the uppermost in place may not always be the uppermost in order. ”

“ Of all the marbles employed in the works of the antients, and of which many specimens have descended to our days, that of Carrara is almost the only one which is at present held in estimation, or is now accessible to modern sculptors. This marble is of a very fine grain and compact texture; it is also susceptible of a high polish when required, and is consequently applicable to every species of sculpture, except when, as is too often the case, dark veins intrude and spoil the beauty of the work. ”