Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/132

granite nor with the schist, nor apparently producing any disturbance in the course or direction of these rocks. They are, as I before remarked, of various colours and compositions, and two veins may often be seen running parallel and in absolute contact with each other, without interference or disturbance, the one of a dark red, and the other of a light grey or some other colour, as represented in one of the sketches.^[1] They are so numerous that perhaps a fortieth or fiftieth part of that region of Cruachan which I examined consists of porphyry veins. The principal varieties both of colour and composition which I remarked, are the following, and their basis consists of that rock which is now by general consent, called compact felspar, but which has at times been designated by the term hornstone.

Brick red porphyry, the base of compact felspar with imbedded crystals of the same colour: a very few specks of white felspar and of greenish hornblende are dispersed through it.

A mixed granular basis of reddish-grey compact felspar, with crystals of a larger size and paler colour, containing also grains of pyrites and long slender crystals of hornblende in abundance.

Base of an uniform dark grey compact felspar with crystals of white felspar.

The same, but with the addition of black mica, hornblende and pyrites.

A grey ground with very large crystals of pale grey felspar; these crystals themselves containing crystals of hornblende. The base contains crystallized mica.

A purple ground with crystals of brownish yellow felspar.

A brown uniform ground with rare and minute crystals of felspar.

1. Plate 6, fig. 2.