464 Dr. Mac Culloch on Quartz Rod. 



and other varieties of primitive schist." Since this paper was 

 originally drawn up, I have seen the country he here quotes, 

 (Arisaik) and have confirmed that his " granitic sandstone" is the 

 rock which I have been describing, and that it is the same rock 

 which he has also described as constituting the ridge of Schihallien, 

 a place of which I shall presently have occasion to speak. Possibly 

 these authors, impressed with the notion that this rock was a 

 ** granular quartz," and that granular quartz was a primitive rock, 

 have not thought it necessary to push their investigations as far 

 as they might have done, nor made the important deductions 

 which must needs follow from this fact if proved. On the geo- 

 logical consequences which would result from its being established 

 it would be useless to speculate till the fact be fully ascertained, 

 as I trust it will be in the sequel of this paper, but it is obvious 

 that it would occasion the removal of mica slate out of the chemical 

 deposits of the Wernerian system, and place it among the me- 

 chanical, or at least the mixed ones : a change which seems to 

 be called for by many other circumstances attending the forma- 

 tion of mica slate. But I must leave this part of the subject for 

 future consideration. 



The true nature of this rock being now, as I trust made out with 

 regard to Jura and the western part of Sutherlandshire, w^e are 

 next led to inquire what evidence there is to prove that all the 

 mountains of " granular quartz" are not of a similar nature, and 

 do not belong to some of the ancient recomposed rocks. The 

 mountains of Scuraben and Morven are cursorily described by 

 Jameson, the former as having a summit of quartz, the latter as 

 possessing the peculiar white aspect so characteristic of the hills I 

 have noticed on the western coast ; and in his work on Geognosy, 

 they are actually quoted as examples of quartz rock. Mr. Pennant 



