Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/329

 not be a little puzzled to reconcile its appearance with that of the surrounding rocks, of which the intricacies already described in this paper, are sufficient in themselves without the further addition of such a deception as this.

It were to be wished that this specimen could be preserved for the future examination of others, but the wants of agriculture must be satisfied, and the pick-axe and spade have already commenced their depredations.

The next appearances in Glen Tilt which I consider worthy of notice, and which are extraneous to the general structure already described, are the marks which it bears of the action of water. If we consider the general characters of the rocks which form the opposite sides of the valley, and attend to the section which accompanies the description, it will be seen that the channel of the river during the greater part of its course, is cut upon the junction of the stratified and the unstratified rocks; in consequence of which those junctions which form so material a part of the interest of this valley have been exposed. It is easy to conceive that a longer continuance of the same action may expose a greater portion of this line, and ultimately lay bare the granite which doubtless lies below the stratified rocks beyond Glen Criny or Gow's bridge down the course of the Tilt. If from future probabilities we ascend to past ones, we may imagine the river once flowing at a higher elevation, and gradually making its way on the surface of the granite and against the edges of the soft strata; the former offering a constant resistance, while the latter, giving way to its action, have formed those precipitous faces the displaced fragments of which have during the progress of time been rolled along the valley to the course of the Garry; being destined in their ultimate progress to assist in forming the immense beds of alluvium which