Dr. Mac Culloch on the Geology of Glen Tilt. 321. 



not be a little puzzled to reconcile its appearance with that of the 

 surrounding rocks, of which the intricacies already described ia 

 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 probabihties 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 j 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 



Vol. III. 2 s 



