Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/429

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419
various parts of Scotland.

high faces of Staffa sink into insignificance on a comparison with the enormous elevation and dimensions of Ailsa. With that elevation is combined an air of grandeur, arising from the simplicity of their aspect, which the pencil and pen are equally incapable of describing. To the lover of picturesque beauty, they possess a requisite, of which the want is perpetually felt in contemplating the basaltic columns of Staffa, or Egg. This is their gray colour, catching the most varied lights and reflections, when the iron cliffs of basalt are confounded in one indiscriminate gloom. He is an incurious geologist, or a feeble admirer of line nature, who is content to pass Ailsa unseen.

This rock is traversed in various parts by large veins of greenstone or basalt. Among these I observed one which was horizontal, but the greater number are vertical, and of large dimensions: these lie on the west side. There is no apparent alteration in the rock at the points of contact. The whole of this island consists of one substance, in which slight differences of appearance here and there occur, but are unworthy of particular notice, and scarcely sufficient to constitute a variety. Its basis is an even and small grained mixture of white felspar, and transparent quartz, in which the former appears to predominate. This mixture constitutes more than three-fourths of the stone, and is mottled by minute and indistinct stains of a black colour, which through the magnifying glass are seen to consist of small grains of hornblende. These appear as if diluted through the stone, and arising from a common centre; and as they vary in proportion to the other constituents, so the rock assumes various shades of colour, from a whitish to a blackish gray, but the lighter varieties predominate.

The stone which I have described may safely be called a syenite, as it accords with Werner's definition of that compound rock, and

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