Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/457



PLATE 14.

This and the six following plates are intended to represent some of the most remarkable circumstances which attend the junctions of the granite with the stratified rocks. They consist of the most interesting portions, and of those which appeared to be the best calculated for explaining the different appearances which are to be seen at these points. With regard to the method used in sketching them, I must add that they are only eye views. Since the greater number of them are represented as if drawn from a point at right angles to the horizon, when they were necessarily taken at an angle often far less than this, it is plain that they will transgress the laws of perspective. But this will produce no alteration in the view they give of the geological facts, however it may derange their graphic accuracy. I have detailed the portions, most frequently, as if they had been detached, although they form in fact parts of continuous rocks. It is plain, when the magnitude of the objects represented, often extending to 40 or 50 feet, together with the minuteness of the fractures which they exhibit, often descending to the tenth of an inch, is considered, that drawings on so small a scale could not be expected to give an accurate detail of all the points in such a space. The leading features however have been marked with as much accuracy as the nature of the subject admitted, and whatever omissions or alterations may have been made, no liberties have been taken which could in any respect misrepresent the facts described in the paper and visible in the places noted.

At the upper end of this figure the granite appears to alternate with the schist. Tracing it further the true nature of the mixture is evident. The portion was selected to show a fact which has been mistaken for an alternation of schist with granite.

PLATE 15.

Represents a disturbance produced in the usual continuity of the schist and limestone, the schistose beds being abruptly broken off at their lower end. It also shows the detached points and lines of granite which are described in the paper, the limestone at the same time bearing indications of its original laminated structure, although the bed is not only here in a vertical position, but its course is also at right angles to the ordinary course of the beds which constitute the southern side of Glen Tilt.

PLATE 16.

Represents the splitting of the limestone bed into three parts, with the intrusion of two masses of granite. A confusion of the granite, schist and limestone is also visible on one side. It further represents the flexure of the limestone and the red lines of granitic matter running parallel to it, of which detached specimens are in the museum of the Society.