part 3] 



LOWER PALiEOZOIC OF AKTHOG-DOLGELLET. 



293 



been derived ; probably, from analogy with somewhat more basic 

 examples of tbe granophyre, the original mineral was biotite. 



Among accessory minerals apatite in very small needles is fairly 

 frequent, also epidote in small granules, occasionally aggregated in 

 little clusters associated witli zircons larger than those usually seen 

 in such rocks. Allanite is relatively not infrequent, partly in 

 prismatic forms, and partly granular, entering into a mosaic with 

 quartz and surrounded by obscure secondary products (fig. 6). In 



Fig. 6. — Sections of allanite, Orogenen granophyre, 

 plane-polarized light. X 50. 



220. 



C 222. 



a. k. w. del. 



one case [C 219] prisms of zoisite were observed radiating from an 

 allanite- crystal. The idiomorphic allanites are, as a rule, strongly 

 zoned and often twinned. Pleochroism ranges from a very pale 

 brown to a rich chestnut-brown. 



As regards the texture observed under the microscope, it has 

 already, been mentioned that this is somewhat variable, and may, 

 as almost invariably in granophyres, alter within narrow limits, 

 according to the relative perfection in which graphic intergrowths 



x2 



