22 , Vol. XLIII., Art. 5.-T. Katô : 



Daijukô area. It strikes almost parallel to the vein, i. e., E. to 

 W., and runs along the walls of the vein, cutting it hero and 

 there. 



The rock is exceedingly altered and bleached. It is white to 

 light greenish white in colour, compact in texture, and contains 

 abundant white phenocrysts of feldspar with a length up to 5 mm. 

 or more. No ferromagnesian minerals are recognizable. Most 

 characteristic is the presence of a fair amount of porphyritic deep 

 red garnet. 



Under tii<^ microscope, the groundmass shows a microscopic 

 granular structure consisting of fine xenomorphic grains of quartz 

 and feldspar admixed with fair quantities of felty fibers of sericite 

 and specks of calcito (PI. III., Fig. 3). No ferromagnesian minerals- 

 are found in the groundmass ; they have been decomposed and 

 have disappeared. Sericite is probably an alteration-product of 

 feldspar, and calcite represents the relics of altered ferromagnesian 

 minerals. 



The most important phenocryst is feldspar, ranging from a 

 microscopic size to several millimeters in length. It is abundantly 

 scattered through the groundmass. It is always entirely altered 

 to kaolin which consists of weakly double-refracting powdery 

 grains and gives rise to a turbid appearance. Calcite in irregular 

 specks is also developed in altered feldspar, mingled with kaolin. 

 Whether the feldspar belongs to orthoclase or plagioclase is not 

 determinable, as it is entirely altered. Both kinds have probably 

 been present. That the plagioclase has been present is indicated 

 by the occasional presence of an altered feldspar showing a zonal 

 structure made up of calcite and kaolin layers. Neither fer- 

 romagnesian minerals nor their decomposition -products retaining 

 the original forms are recognized as phenocrysts. Irregular flecks. 



