SYNOPSIS OF GNEISS. 



D. A schist of foliated mica, with interspersed and large 

 irregular crystals of felspar; the quartz being scarcely 

 discernible. 



It may be added that the whole of this subdivision 

 present transitions from gneiss into quartz rock and into 

 micaceous schist. Where the felspar is red they are easily 

 distinguished : when white, it is much more difficult to 

 recognise them. I may also add that hornblende is, as 

 in the first division, an occasional ingredient. 



This variety occurs abundantly on the west coast of 

 Scotland, in Rannoch, and in the middle Highland districts 

 of Atholl and Badenoch. 



THIRD SUBDIVISION. Laminar. 



In the two former subdivisions, either the whole mass 

 has a granular structure combined with the foliated, the 

 latter arising from the position of the mica, or the horn- 

 blende ; or else the quartz and felspar form one granular 

 mass, separated into laminae more or less defined, by the 

 mica, or by the hornblende. In the present, each substance 

 occupies a distinct lamina, the quartz and the felspar being 

 separated ; sometimes remaining in contact, at others being 

 divided by intervening laminae of mica or of hornblende. 

 This variety is generally remarkable from the contrast 

 and disposition of the substances, and the quartz fre- 

 quently puts on the muddy aspect of chalcedony. 



* A. Quartz and felspar in alternating laminae. 



B. Quartz, felspar and mica, similarly alternating. 



C. Quartz, felspar and hornblende, disposed in the same 



manner. 



* D. Felspar and hornblende in alternating laminae. 



The varieties A, B, are abundant in Glen Elg, Rona~ 

 and Ardgower; the third occurs occasionally in various 

 situations. The quartz is also found alternating with mica 



* These might with perhaps more propriety be placed in the thiid 

 division. 



