Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/233

 greenstone. This variety is the least abundant. It occasionally assumes a brownish or reddish colour, retaining its original compactness and uniformity of texture, and thus forming a member of the trap family, to which no distinct name has been assigned. This becomes at times porphyritic, containing numerous minute crystals of felspar imbedded in a blackish or brown basis, and forming a showy variety of trap porphyry. The felspar, as far as I have observed, is always opaque. Sometimes the rock is both porphyritic and amygdaloidal, but perhaps the greater part of the whole hill consists of a rock merely amygdaloidal, the base of which is either the well characterized basalt above described, or that variety which is less marked, or else a rock intermediate between this latter and indurated clay.

The character of the amygdaloid varies considerably according to the substances which it contains, and these are green earth, calcareous spar, quartz, and chalcedony.

Green earth or chlorite, is the substance which perhaps occurs most frequently, and it is indeed that by which the trap of Kinnoul is particularly distinguished from almost all the rocks of this tribe in Scotland. The nodules vary but little in size, and although they are occasionally met with of the bulk of a filbert, they are generally little larger than a grain of mustard. But they vary much in colour, assuming all shades from greenish black to the brightest verdegris green. They differ equally in texture, being sometimes minutely powdery, at other times of a large scaly fracture, like the chlorite which occurs in primary rocks. It is this substance which Faujas has called steatite; no real steatite being found in the trap of Kinnoul, although it is common in that of the island of Sky.

When calcareous spar forms the amygdaloidal nodule, it is commonly invested with a coating of chlorite. These nodules are