Copper-Tin Veius of the Akénobé District. 21 



•crystals of hypersthene, usually less than 2 mm. in length, are 

 sporadically found. 



Under the microscope, the groundmass shows a hyalopilitic 

 structure consisting of very minute feldspar laths, often in fluidal 

 arrangement, and a devitrified glass-base mixed with aljundant 

 minute specks of calcite, mostly representing a decomposition- 

 product of ferromagnesian minerals (PI. III., Fig. 4). In fresh 

 specimens a brown glass-base is present, cementing the feldspar 

 laths and contaminated with minute grains of diopsidic augito. 

 Minute crystals and grains of magnetite are scattered through the 

 groundmass. Some ilmenite is evidently present as the presence 

 of leucoxene, developed along the border of a few grains of black 

 opaque iron ore, suggests. 



Porphyritic plagi(3clase is always characterized by polysynthetic 

 twinning and is tabular in habit. Its refraction is far higher than 

 that of Canada balsam. The maximum symmetrical extinction 

 (ca. 35^) shows that it belongs evidently to the soda-calcic group, 

 i.e., the labradorite-bytownite series. While the plagioclase pheno- 

 crysts are very abundant, ferromagnesian minerals are very sparse. 

 Only s])oradically are hypersthene crystals found with the naked 

 eye. In addition, diopsidic augite, in small prismatic crystals, 

 is sparingly distributed in fresh specimens. This rock, then, may 

 be classed as two-pyroxene andésite very poor in ferromagnesian 

 minerals. 



Garnetiferous Fehlte- Porphyry. A light-coloured, garnetiferous 

 igneous rock in the form of a dyke is exposed at the stream 

 bottom near the meeting point of the Fadono road and the 

 Mikobata road at the village of Akénobé. It is about 3 meters 

 thick and strikes N. E. A similar garnetiferous dyke was dis- 

 covered in the underground working in the Ebisu adit in the 



