Ch. V.] PRIMARY SCHISTOSE ROCKS. 61 



This mica-slate is in most places traversed by layers or 

 beds of quartz rock, of various forms and dimensions ; and, in 

 addition to the minerals already mentioned, it incidentally 

 contains andalusite, garnet, and sphene.* 



On the southern part of this primary range, as already 

 stated, the granite is not bounded by mica-slate, but by clay- 

 slate, which is described by the same author as being yellowish, 

 greenish, or purplish in colour; smooth, glossy, fissile, and 

 free from admixture : but in general it is so blended with the 

 rocks with which it is associated, that its true nature can only 

 be understood after considering all its various relations. These 

 rocks are clay-slate, conglomerate, greywacke*, greywacke- 

 slate, quartz rock, greenstone, and greenstone porphyry. 



" The clay-slate conglomerate consists of angular fragments 

 of clay-slate, some nearly as large as the head, with smaller 

 fragments of quartz, imbedded in and cemented by clay-slate." 



" The greywacke is composed of small rounded and angular 

 grains of quartz, numerous minute scales of white mica, small 

 fragments of clay-slate, and sometimes portions of felspar 

 cemented by clay-slate. The grey wacke-slate is a similar rock, 

 with a slaty structure ; and it is the predominating rock."f 



" The quartz rock is generally white or yellowish-white, 

 but is sometimes more or less stained with yellow, red, and 

 brown. In its structure, it varies from the perfectly compact 

 splintery to the close-grained granular ; sometimes contain- 

 ing small, well-defined, rounded grains of quartz, which are 

 frequently of a different colour from that of the base ; but it 

 contains very rarely rounded and angular grains of felspar, 

 and a few scattered minute scales of mica. Such is the cha- 

 racter of the pure quartz-rock : but it is not only interstrati- 

 fied with clay-slate on the large, but on the small scale ; and 

 it is in these alternations that reciprocal incorporation takes 

 place, presenting rocks in some instances of a homogeneous 

 character, and in others of a distinctly compounded structure. 



* Geol. Trans., vol. v. p. 154 f Idem, p. 165. et seq. 



