Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/425

Rh map in the possession of the Society, founded on the general opinion of the mineralogists of Scotland, calls it a flœtz limestone.

A very cursory survey of it is sufficient to show, that it consists of irregular and broken fragments of beds disposed in every possible position. Occasionally it is flat, but is now and then elevated at a small angle, and often appears as if it consisted of strata perfectly vertical. Almost every where it is disturbed and contorted to a great degree. The beds are easily traced in several places, where quarries have been dug, or mines wrought; and in many others the inclination of the soil and the action of water, have laid the edges bare for some hundreds of yards together. The perfect similarity of its disposition to that of the limestone which accompanies clay slate all over the Highlands of Scotland, and more particularly to that of the island of Lismore, would suffice to determine its true character, even without the detail of specimens. There are two predominant varieties of it. Of these, one is dark blue, and the other greyish white. They are both compact, and hard, but the aspect of the whiter varieties is more crystalline than that of the dark, which indeed often possess a merely earthy and granular appearance. In many places the blue varieties, where most crystalline, are traversed by numerous veins of a white colour, producing an ornamental marble worthy of attention.

The blue varieties of this limestone appear to be deposited in contact with clay slate, the white on the contrary, which are much more rare, are found in contact with a micaceous slate.

When the blue variety approaches the clay slate, it first assumes a schistose fracture. Shortly after it appears penetrated with delicate laminæ of straight or undulating silky schistus, which by degrees increase in number, and at length so predominate, that it is only by examining the cross fracture, and even with some care, that the