364 ON THE HIGHLANDS. 



pects, and at other places, with hornblende-rock, 

 and hornblende- slate. In this part of the forma- 

 tion, the matter of hornblende prevails so much, 

 as often to colour, not only the substances com- 

 posed of quartz and felspar, but even the mica- 

 ceous strata themselves. The connection, in- 

 deed, which exists here, between the hornblende 

 and mica- slate, resembles so nearly what is men- 

 tioned by Von Buch, as occurring in the envi- 

 rons of Landeck, that I cannot describe it more 

 exactly than by quoting his description. " Mi- 

 ** ca-slate is often seen to pass into hornblende : 

 " the mica -slate begins to be changed into a rock 

 " of a deep greyish-black, which is an intimate 

 " mixture of quartz and mica ; then it becomes 

 " harder and more difficultly frangible ; the mi- 

 44 ca by degrees giving place to the hornblende, 

 " which at last preponderates. At other times, 

 " we do not observe the passage of the one into 

 " the other, and it is simply a bed (with a base 

 " of hornblende) of considerable thickness in the 

 " mica- slate Iron-pyrites is an ingredient 



that pervades occasionally all the rocks to which I 

 allude. 



At length, a mass of the granular aggregrate 

 now described, which is of great size, and 

 which Professor Jameson suspects to be Sienitic 

 Greenstone, shews itself in the bed of the 



* Translation by Dr C. Anderson, p- 33. 



