SYNOPSIS OF GNEISS. <23 1 



SECOND SUBDIVISION. 



Consisting of compact felspar united to the ordinary 

 ingredients of gneiss. In structure it sometimes resembles 

 common gneiss, but more frequently its fracture is like 

 that of the non-fissile schists, presenting no indication of 

 laminae. 



A. Compact felspar with hornblende. 



B. The same with hornblende and mica. 



C. Compacted and compact felspar united. 



D. A granular and laminated mixture of compact felspar of 



different colours. Perhaps this rock should rather 

 be arranged with the compact felspars. 



E. This includes those varieties of gneiss formerly de- 



scribed, in which compact felspar is superadded to all 

 the ordinary ingredients. 



The substances ranked in this subdivision are frequently 

 traversed by veins of compact felspar, often reticulating 

 in an intricate manner, and so numerous as to form a 

 large proportion of the rock. The predominant colours 

 in this compact felspar are various shades of grey, but 

 the green variety formerly described is also very common. 

 They occur abundantly, sometimes in connexion with the 

 varieties of the first subdivision, in Sutherland and Ross- 

 shire; and are particularly conspicuous on the borders 

 of Loch Mare, where they are associated with a fine 

 hornblende schist that occasionally passes into a sub- 

 stance scarcely distinguishable from the argillaceous slates. 

 They have already been pointed out in North Uist and 

 West Rona. 



THIRD DIVISION. 



Of irregular composition, being either deficient in the 

 number of ingredients required to meet the definition of 



