Copper -Tin Veins of the Akénobé District. 



47 



in alternation with quartz crusts. The most characteristic arrange- 

 ment of the layers in the ring-ore in question, as observed in thin 

 sections, is shown in Fig. 11. The first crust is composed of 

 hypidiomorphic crystals of cassiterite which are frozen to the 

 silicified rock-fragment ; the second crust is composed of quartz 

 grains containing sporadic cassiterite crystals ; the third crust is 

 made up again of cassiterite crystals ; the fourth one consists of 

 large grains of quartz, on the outside of which a broad crust 

 consisting of wolframite plates, cassiterite crystals and quartz grains 

 is developed. In places, these cassiterite -bearing bands unite 

 together and form a wolframite-cassiterite-bearing layer, which is 



deposited directly on the rock-frag- 

 ment. The quartz layer containing 

 wolframite and cassiterite frequently 

 shows indistinct radial fibrous or 

 radial bladed structure, representing 

 probably an advanced stage of 

 transformation of opaline silica to 

 quartz. 



Microscopic topaz in the Daisen 

 vein. The writer found, in the course 

 of microscopic examination of many 

 thin sections of the quartzose wolf- 

 ramite -cassiterite ore from the Daisen 

 vein, several microscopic crystals of a 

 colourless mineral. They are embedded in quartz, usually pris- 

 matic in habit and frequently showing terminal faces (PL VII., 

 Fig. 2). The size ranges from 0.15 to 0.5 mm. in length, no 

 macroscopic crystals having yet been found. 



The mineral shows straight extinction and fairly high re- 



Fig. 11. Ciimera iucida drawing of 

 a part of the ring-ore from the Sekiei 

 vein. Enlarged abont 10 diameters. 

 S, Bilicifie 1 rock-fragment ; T, tin- 

 stone ; Q, quartz ; W, wolframite. 



