Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/131

 of Loch Ranza, yet in many places they are intermingled with it in a very remarkable manner. 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. In many instances these fragments either exhibit at their edges a change into a substance resembling basalt, or are actually converted into a black matter which has at first sight the aspect of a fine grained hornblende rock or a basalt of the blackest hue, and which only an accurate inspection discovers to be modified fragments of schistus. The schistus in general which lies in the immediate vicinity of the granite vein is highly indurated and gives fire readily with steel: in other respects it retains its general character, a laminated structure and alternating stripes of colour.

Independently of the peculiarities now described which characterize the junction of the granite with the schist at this place, the passage of the porphyry veins may be observed in great perfection, and as they form an important feature of the character of Cruachan and occur in all parts of it, I shall here describe them at some length.

These veins are of different sizes as well as aspects, varying from the breadth of three or four feet to that of fifty, or more: they are all very erect, and in a general view appear perpendicular. They traverse both the schist and the granite, and are to be observed in this part of the hill, cutting the vein equally with the schist in all directions, as may be seen in the accompanying sketches. They are uniformly well defined, neither intermixing in any respect with the