292 Dr. Mac Culloch on the Geology of Glen Ttlt, 



distinguished in the generality of hand specimens from genuine 

 granite : at the same time I must add, that it bears but little resem- 

 blance to veins. The neighbouring rocks furnish abundant ex« 

 "^mples of ordinary granite veins, which are readily distin- 

 guished from the present appearances by the decision of their 

 junctions, while in this case a regular gradation exists between the 

 ■granite and the schist, and no boundary to the former can be as- 

 signed. The appearance which I have now described is not limited, 

 as I have just said, to this place : other examples of it may be found. 

 Besides the loose specimens of it which are to be observed among 

 •the transported blocks on the hills which bound the left side of the 

 valley, it is also of frequent occurrence through a large tract which 

 extends from Blair to Dalwhinnie, and thence to the head of the 

 Spey. The specimens seen in this direction frequently exhibit va- 

 rious and repeated alternations of granite and schist, from the thick- 

 •ness of three or four inches down to that of a quarter of an 

 inch. The tract in question is wholly, or in a great measure, com- 

 posed of hard argillaceous schist, graduating into schistose quartz 

 rock and more rarely into micaceous schist, with granite veins dis- 

 persed here and there through It. Between the laminse of these 

 schists the granite is found graduating into the schist, many varie- 

 "tles of coarser or finer texture appearing in rapid succession 

 in the space of a few inches. It Is only by the comparison of a 

 'number of specimens that the true nature of the rock is discovered, 

 and it affords a curious example of the facility with which false 

 conclusions may be formed on this intricate subject. However pa- 

 rallel the lamlnse of granite may be to those of the schist for a 

 certain space, they invariably quit that direction when the specimen 

 Is of sufficient magnitude, "and may be seen holding an oblique 

 course through these laminae, often indeed becoming true granite 



