Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/441
any change of their direction or appearance, marking clearly a common condition in the schist and the quartz, at the period of their formation. It is also worthy of remark, as I have observed, in another place, in speaking of the rutile of Killin, that although the crystals of disthène in general penetrate and impress the quartz, they are sometimes bent and waved as if they had accommodated themselves to its irregularities. Ignorant as we still are of the mode in which various minerals are crystallized together, it is not unworthy of our attention to collect all the facts which may tend ultimately to throw light on this obscure process.
The clay slate which I have mentioned above, constitutes a large portion of the mountains which here form the termination of one of the Grampian branches in this direction; it is succeeded by a hard quartzy sandstone, similar to the rock of Assynt, before described, and by an exceedingly hard quartz breccia, in which the paste is red, and the fragments white, and which is noted for containing agates and jaspers. Immediately after this follows the red sandstone, which constitutes a great part of the flat tract of Moray, and bounds the course of the Spey in this place. It is accompanied by the singular rock above alluded to, which I am about to describe. This rock consists of a talcy clay slate, so penetrated with hornblende as to render its character for an instant doubtful. On an accurate examination, it will be seen that the body of the rock is a clay slate, and that it is interspersed throughout with lamellar and thin crystals of hornblende. These lamellæ are generally disposed at right angles to the lamellæ of the schist, and are sometimes short and straight, and variously placed, interfering with each other in every direction. More commonly they diverge from a sort of central axis, in curved planes, so that their section according to the lamellæ of the schist, exhibits an appearance