John MacCulloch

“ Crystals of the hornblende may be observed shooting far into the body of the schist, so as to render it often difficult to assign the limits of each rock. In a less degree the quartz and felspar exhibit the same appearance. Together with this, the schist is singularly contorted, being bent, broken, and intermingled in a most confused manner with the rock that traverses it, while distinct detached fragments are often involved in the mass of granite. ”

“ The rugged forms and rocky faces characterizing those hills of mica slate which bound Loch Lomond, Loch Long, Loch Fyne, or Strath Fillan, have disappeared; the mountains assume a more uniform flowing line, their sides are more completely covered with herbage, and exhibit fewer denuded rocks; their summits are less serrated, and are almost the only parts which exhibit the naked rock, while at the same time they are strewed with heaps of fragments, a character from which the hills of mica slate are almost always free. ”

“ I attempted in vain to find it on the flat tract at Bunawe, nor did I succeed any where from Tyanuilt to the sea in recovering any portion of this stratum; the low land being always covered with alluvial matter, and the denuded rocks appearing every where to consist of schist and granite traversed by veins of porphyry. It affords a remarkable example of a deposit of secondary rock, not many hundred yards square, entangled in the middle of a primary district, and separated, apparently by many miles, from any other similar rock. ”

“ As we ascend to cross the foot of the hill granite appears exclusively, generally in the shape of loose blocks accompanied by similar pieces of porphyry, but sometimes in situ. On reaching the shore beyond Bunawe the appearances become more interesting. The junction of the granite with the schistus is here clearly seen. Large veins may be observed proceeding from the great mass of the mountain, and ramifying into innumerable small divisions penetrating and traversing the schistus in every direction. ”

“ In some cases dark blueish specimens are found veined with red, producing very beautiful and remarkable varieties: in others, the red colour is so bright, and the texture so compact, that they can scarcely be distinguished from jasper, a rock which, I may remark, although hitherto but little examined in its geological relations, possesses a very near affinity to the family of porphyry, as well in the extensive independence of its position among the regular rocks, as in its appearance and composition. ”

“ To the north it presents a range of nearly perpendicular precipices extending many hundred feet down the mountain. The mass of the mountain is easily seen from this point to consist of granite. This appears to be of uniform composition on both the summits, and to be formed of a very equal mixture of reddish felspar and white quartz with very little mica, nearly resembling the granite of Cairn Gorm. The porphyry veins which traverse it are here also as visible as they are below, but if there is any difference they appear of greater magnitude, and the red variety predominates. ”

“ Veins of perfectly characterized basalt also occur in some places, and these, or fragments of them may in particular be observed in great quantity strewing the top of the first summit, (that one which is marked by two cairns,) and laying fair claim to an equal antiquity with the veins of porphyry. It is easy to procure detached specimens of the junction between the granite and basalt in great variety and abundance. The line of junction is in all cases clear and well defined, but does not admit of ready separation even after long exposure to weather. ”

“ Although the naked surfaces of these rocks might lead us to suppose they were inimical to vegetation, this effect must rather be attributed to the steepness of their declivities, which prevents the accumulation of soil. From whatever cause it may arise, they seem particularly subject to be destroyed by the action of the mountain torrents, whence the enormous piles of fragments which annually overwhelm the road and are fast raising the level of the valley. ”

“ It is equally familiar to those who visit Oban, since the surrounding country and the neighbouring islands are covered with more or less extensive masses of it, in some cases reposing on the older schists, which form the visible basis of this country, in others upon the sandstone strata already described. It is in this latter case that it produces the effect already alluded to of partially concealing the masses of sandstone, so as to give an appearance of separation where no real one exists. ”

“ In many places there is an appearance of veins proceeding from the mass, rendered conspicuous by their projection and superior durability, but in examining the surrounding rocks where in contact with them, no difference of structure or composition is perceptible. ”

“ The masses vary in size from an inch to a foot and upwards, but whatever their size may be they have almost invariably parallel sides. The examples of this appearance are very numerous both at Balahulish and in the rolled fragments of granite which are spread over the Black mount to the eastward of Glenco, and we shall presently see that the same granite with similar connections occupies a very large tract of country. ”

“ In quitting this part of the skirt of Cruachan it is necessary either to rise to a considerable elevation, crossing above the woods of Inverawe, or to avoid it altogether and make a circuit by Bunawe. We then reach the shore of Loch Etive, and may continue our observations on the base of the mountain. ”

“ Their continuity and extent as they occur on the eastern and southern skirts of the highland mountains are too well known to require notice, and they will be found to occupy an extent similarly continuous, as far as geographical circumstances will permit, on the north-western coast of Scotland and in the islands connected with it. ”