158 MICACEOUS SCHIST. 



curs also i:i very limited beds, alternating with other 

 strata, as a portion of sonic complicated scries; while, 

 further, it occasionally intrudes as an incidental sub- 

 stance, where the predominant series belongs to an- 

 other family. 



It is found in contact with granite in Arran ; form- 

 ing a mass of considerable dimensions, and, allowing 

 for its insular position, connected with the most ex- 

 tensive range of the same rock in Scotland. The 

 granite which ranges from Appin to Rannoch, is also 

 often covered, on its southern boundary, by micaceous 

 schist, occasionally intermixed with quartz rock and 

 argillaceous schist ; this contact being the northern 

 margin of that great tract, the southern limit of which 

 reaches to the shores of the Clyde. Extensive ex- 

 amples of the same junction occur also in Perthshire, 

 in Sutherland, in Aberdeenshire, and in Shetland. It 

 is interesting to remark, that where thus in contact 

 Avith granite, it often assumes the character of gneiss 

 for a small space, by acquiring felspar ; but this 

 change is always limited to a short distance from the 

 contact, or to the portions traversed by the granitic- 

 veins. The fragments entangled in the granite are 

 also often converted into the same substance ; under 

 an obvious analogy to the change from argillaceous 

 to micaceous and hornblende schists in the same 

 circumstances. 



As already remarked, micaceous schist succeeds to 

 gneiss through a very considerable part of Scotland ; 

 alternating with it by such frequent interchanges, 

 that the limits cannot be accurately defined, and 

 forming also occasional beds within it. I have also 

 shown that it does not necessarily follow this rock : 

 which is succeeded, in at least an equal degree, by 

 many others of the primary strata. As it is intimately 



