18 Vol. XLIir., Art. 5.— T. Katö: 



characterized by its perfect cleavage and strong pleochroism, winö 

 yellow to dark green, occurs in minute flakes enclosed in feldspars. 

 Sometimes it occurs in hypidiomorphic flakes attached to the well- 

 defined borders of the feldspars, showing its subsequent crystalliza- 

 tion. Minute flakes of chlorite, evidently a decomposition-product 

 OÎ biotite, is sparingly scattered through the rock. A small quantity 

 of secondary epidote, very slightly pleochroic, yellow to colourless, 

 and cliaracterized by speckled inteiference colours, is present in 

 the form of streaky aggregates along the cracks of feldspars, or in 

 irregular patches replacing the same minerals, or in flakes over- 

 lapping quartz grains in the cementing matter. 



The leucocrate, here considered, shows in places a typical 

 aplitic structure, being fine-grained, rather equigranular, and con- 

 sisting of rounded grains of quartz and hypidiomorphic and 

 xenomorphic feldspars (botli oligoclase and orthoclase) and a fair 

 quantity of green biotite in minute flakes. A gradual transition 

 fr.)m one structure to the otlier may always be observed. 



To this peculiar leucocrate, corresponding in mineral- com- 

 position to quartz-monzonite-pegniatite or aphte, the writer gives 

 the name of ' akenobeite.' It is the only acid granular rock found 

 in this vein district, and it is particularly noteworthy that it is a 

 differentiation-product of the diorito magma. 



All the dioritic rocks in this district, hitherto described, are 

 derived from the same source, and erupted during the same period, 

 probably a late Mesozoic age. The main intrusive mass forms the 

 southern and eastern parts of the Akénobé- district, while the 

 offshoots are found here and there in large dykes and bossy masses 

 throughout the vein district. Some of the offshoots are evidently 

 of later intrusion than the main mass, liaving been derived from 

 the unconsolidated portions of the same magma-basin. It is worthy 



