^66 Dr. Mac Culloch on the Geology of Glen Tilt, 



manner. Such is the ordinary view which has been taken by one 

 class of observers of this rock, as well as of all the other rocks seen 

 an Glen Tilt. They have been looked upon as mere masses of 

 -schist intersected by veins of granite, the larger bodies of granite 

 bein^ considered as vein^ the origin and direction of which were un- 

 known, and the smaller ones as ramifications proceeding from them. 

 A different class of observers, seeing in this imagined schist 

 nothing but its approximate position with granite, have considered 

 it as offering an example of the alternation of these two rocks. In 

 whatever way the different theories may be affected by these dis- 

 tinct views of this case, I have no inclination at present to enquire. 

 If one of them be incorrect, the other is imperfect, and the object 

 of this paper is rather to give a more full account of the appear- 

 ances to be observed in this place, than to renew a controversy on 

 the same grounds on which it has already been agitated. 



Independently of such <:onsiderations, the disposition of the 

 rocks at this place, as well as in other parts of the Tilt, are so 

 curious, and as yet so solitary and new, as to render them highly 

 attractive and well worthy of record. It will however be seea 

 hereafter, that the history of these several appearances, even if it 

 should not be supposed to add any strength to the general theory- 

 respecting the posteriority of granite, serves at least to give us au 

 accurate idea of the real structure of the valley itself. 



The remarkable novelty here visible, and in which the junction 

 of the granite with the superincumbent rocks differs from all similar 

 junctions formerly described, is that of the interference of granite 

 and limestone. The granite veins which traverse the schist, pass 

 equally into the limestone which accompanies it. These veins are oc- 

 casionally of large size. In this case they can sometimes be traced into 



