362 ARRAN. GEOLOGY. SCHIST. 



respecting the schists of Arran, considered as specimens 

 only, will now be seen to have arisen from imperfect 

 views of their geological affinities and position ; combined 

 perhaps with some hypothetical notions respecting the 

 characters which ought to exist in those rocks that 

 approximate to granite. Had the two sets of strata 

 above mentioned been studied on the mainland, and 

 the double series been extended, as is here done, to 

 this island, no such confusion would have existed. 



In the first series, that of the micaceous schist, which 

 occupies the chief part of the schistose tract on the 

 western side of the mountains, this rock occurs under 

 the usual diversity of aspect, which it would be super- 

 fluous to detail after the remarks on this subject formerly 

 made. Occasionally, as in the more regular parts of the 

 series, it also graduates into talcaceous and into chlorite 

 schist. In some places it passes into, or perhaps rather 

 alternates with argillaceous schist, and at these points 

 probably, the obscure boundary, already described, between 

 the micaceous and argillaceous series, exists. In the 

 tract under review, these transitions will be found to 

 occur principally near the source of the Machrie water, 

 where the common limit of the two is indicated in 

 the map. 



There is much more variety in the argillaceous series. 

 Near the whole of the junction before described, which 

 extends from Glen eas na birach to Glen Catcol, the 

 schist is argillaceous, but generally of uncommon hardness, 

 and often interlaminated with quartz in such a manner 

 that the argillaceous ingredient is at times nearly ex- 

 cluded. In a few places it presents the more ordinary 

 characters. It is followed by chlorite schist, passing 

 into micaceous and into talcose schists ; the whole being 

 so irregularly intermingled that it is impossible to define 

 their several boundaries. All these varieties are, as 

 in Bute, sometimes of a granular, at others of a simple 

 laminar structure ; and their general resemblance to the 



