Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/281

 rhomboidal tables. In this respect it bears a considerable analogy to the clay slates with which it is so often associated.

Among the varieties found in Ben Gloe I remarked some others worthy of notice, considering the novelty of this subject and the necessity of describing every remarkable feature of a rock so long overlooked or confounded with others. The most singular of these is of a beautiful pink colour, equal to that of the well known rose quartz, with the semi-transparency and fine grain of the most highly refined sugar: it forms interesting specimens for collectors of minerals. I have mentioned it in describing Glen Tilt. Another is of a dark brown colour, apparently from containing much carbonate of iron, but when it is exposed to the weather the surface is bleached to the depth of a quarter of an inch and becomes of a snowy whiteness. A third is of an ochre yellow colour and loose texture, and in hand specimens not to be distinguished from a common secondary sandstone, while at the same time it contains distinct concretions of crystallized carbonate of lime irregularly dispersed through it. A variety equally resembling some of the secondary sandstones which occur among the coal strata in the vicinity of Glasgow and elsewhere, is found near Balahulish. It is distinguished by the frequent alternation of black laminæ, of which the cross fracture represents delicate lines, and it serves with others already enumerated to confirm the strong affinity of the recent sandstones with quartz rock, the sandstone of former ages.

Among the various modifications of quartz rock which I have observed in the different districts now described, a great many exhibit the characters of the avanturine, the quartz avanturiné of Brongniart. I have frequently noticed the transition which takes place between quartz rock and mica slate, a transition so gradual and so perfect that it is often impossible to assign the limits of the two. The quartz