Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/447

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437
various parts of Scotland.

is, however, intermixed with rocks, consisting of hornblende, and felspar, and of micaceous schist mixed with hornblende. It exhibits therefore, specimens of the syenite of Werner, but such as are evidently associated with the mica slate family, and perfectly distinguished in their connexions, from the greater bodies of syenite occurring in Scotland, which appear in an independent position, resembling that of the trap family. The mica slate is often remarkable for containing numerous and very large cubical crystals of pyrites, an occurrence much less frequent in this rock than in clay slate.

Veins of quartz traverse it in innumerable places, and it is also interspersed with compressed nodules of quartz, which bear no marks of attrition, but are intimately united to the mica slate, or chlorite slate, in which they occur. They are frequently characterized by a beautiful transparent brown colour, which renders them objects of much research and high price among lapidaries.

Massive chlorite also appears in abundance, and it is generally interposed between the chlorite slate and quartz nodule. But the object for which I have chiefly noticed this mountain, is the occurrence in it of Rutile, a mineral as yet of sufficient rarity to deserve a record of all its habitats. It is found in the larger, as well as in the smaller quartz nodules, and exhibits many of its well known varieties.

The crystals generally penetrate the quartz, and often appear to have their bases fixed in the investing chlorite. It is worthy of remark, that although they most commonly penetrate the quartz, as if crystallized at perfect liberty, yet they are frequently bent, so as to accommodate themselves to its occasional elevations and depressions.

Our knowledge of the chemical laws by which mixed minerals are crystallized together is as yet so imperfect, that we can offer no conjecture on an appearance so complicated as this, which however, is not the less deserving of our attention.