PLATE XLVI. 



FIG. 1. 

 QUARTZITE. 



LICKEY. 



Magnified 55 diameters. Nicols crossed. 



This represents fig. 2, Plate XLVL, under crossed nicols. The secondary 

 quartz (A) is seen to split up into distinct portions which are in optical continuity 

 with the adjacent grains (B and C). The individual grains are sometimes 

 uniform in their optic properties (C) and sometimes consist of two or more 

 distinct portions (B and D). 



FIG. 2. 

 SCHISTOSE QUABTZITE. 



KKRIBOL, SUTHERLAND. 



Magnified 25 diameters. Nicols crossed. 



This figure is an attempt to represent the appearance of a quartzite which 

 has been affected by dynamic metamorphism. 



The relics of the original grains (A) give undulose extinction and lie in a 

 crypto-crystalline aggregate (B), apparently formed by the crushing of the 

 original constituents. Planes of schistosity in the rock are seen, under the 

 microscope, to correspond to bands entirely composed of the crypto-crystalline 

 material. One such band traverses the figure from left to right. These bands 

 represent the extreme of mechanical metamorphism so far as the quartzite is 

 concerned. 



This figure must not be looked at too closely. A fine diagonal striation 

 which is not visible in the section has been represented as crossing the central 

 band of crypto-crystalline material. 



The rock from which the section has been prepared was collected by the 

 author under Prof. LAPWORTH'S guidance in the summer of 1888. 



