Ch. V.] PRIMARY SCHISTOSE ROCKS. 59 



in which these are united. Thus it has been shown that one 

 insulated patch of Cornish granite is very felspathic and 

 abounding in porphyry ; another, shorlaceous, and containing 

 numerous beds of protogine (china-stone) ; and a third, more 

 micaceous than ordinary, and intersected by layers of eurite ; 

 and in each of these cases we have seen that the series of ad- 

 jacent schists vary accordingly, and yet each series may be 

 considered as the equivalent of the other. 



Now let us proceed to examine the nature of the crystalline 

 slates of other countries, and to enquire whether they bear the 

 same relations to the accompanying granite, as obtains in 

 Cornwall; or whether these rocks, in the latter case, are 

 exceptions to the general rule, and have a peculiar arrange- 

 ment. 



In Ireland it has already been stated that the extensive 

 mass of granite occurring in the eastern district presents a 

 difference of composition in its northern and southern portions : 

 in the former, it consists of the ordinary ingredients, being 

 often quartzose, but exhibiting little variation of mineral 

 character ; whilst in the latter, quartz is not so abundant, and 

 the felspar and mica are sometimes intimately incorporated, in 

 some varieties resembling homogeneous trap, and in others 

 verging towards clay-slate ; and, in like manner, the adjacent 

 schist is principally mica-slate in the north, and clay-slate 

 in the south. 



" This mica-slate," says Mr. Weaver, " wherever it occurs, 

 is in direct contact with the granite. It consists of alternate 

 layers of quartz and mica, from one line to two and three 

 inches thick, and some layers of quartz extend even to two 

 feet in thickness, while the surface of the intervening mica is 

 almost invariably studded with cruciform and stelliform aggre- 

 gations of hollow spar."* " The mica-slate which occupies 

 the lower part of Glenmacanass, on the western side, contains 

 a bed of talc-slate, of uncertain thickness, both rocks dipping 

 25 towards the south-east. The talc-slate is of a greenish 



* Geol. Trans., vol. v. p. 140. 



