GEOLOGY. 15 



Mica-Slate or Schist, which, as possessing more mica and 

 being of a more slaty structure, is so denominated. This rock 

 is readily distinguished from gneiss by its glistening aspect, and 

 from granite by the absence of felspar, although it occasionally 

 seems to graduate into both when in contact. The particles of 

 which it is composed are uniformly more broken and rounded 

 than those of gneiss, which probably arises from their being 

 partly derived from the granite and partly from the gneiss, 

 and have in consequence undergone a double process of 

 attrition. Veins of quartz, parallel with the strata or crossing 

 them in every direction, are so predominant often as to 

 change the usual colour from a glistening grey into a mottled 

 white. Vertical dykes of the purest quartz, sometimes 

 several yards in breadth, and traceable for miles along the 

 surface, are likewise of frequent occurrence. One variety is 

 termed garnet-schist, from the circumstance of these beautiful 

 crystals being so abundantly distributed through the substance 

 of the rock as to foi'm a principal ingredient, as well as greatly to 

 enhance the sparkling lustre of the mica. The garnets vary from 

 the size of a small seed to an inch in diameter, are of a dark 

 crimson colour or blackish brown, and under a bright sun look 

 like gems in a setting of gold. They occur plentifully in the 

 formation near Huntly, in the upper districts of Strath Tay, and 

 of considerable dimension and very perfect in the Isle of Mull. 

 The geographical distribution of this rock is much inferior in 

 extent to the gneiss : it is chiefly confined to the more central 

 division of the Grampians, which it accompanies in one con- 

 tinuous envelope, along the range from sea to sea. The mica- 

 schist thus embraces within its course the finest and most 

 celebrated scenery of the Highlands. No lover of the pictur- 

 esque, in his most favoured haunts, can fail to recognise it, 

 whether by its bright metallic aspect or the remarkable flexures 

 into which the strata are twisted and folded up. Suffice it to 

 mention the beautiful ravines on the Esk and Isla, the Pass of 

 KiUiecrankie, the Trosachs, the charming environs of Loch Ket- 

 terin and Loch Lomond, the precipitous defiles of Glencoe, and 



