^2 ^'ol. XLIIL, Art. 5.-T. Kiitj: 



Under the microscope, the rock is found to bo ahnost entirely 

 composed of tine anhedral grains of quartz, and shows a quartzitic 

 structure, penetrated irregularly by microscopic veinlets consisting 

 of somewhat larger grains of quartz (PI. IL, Fig. 3). 



The reddish brown veinlets cutting the silicified slate are 

 revealed, under the microscope, to consist of siderite and limonite, 

 the latter mineral being an alteration-product of the former. It 

 is evident, therefore, that the silicification took place prior 

 to sideritization. This will be fully considered in a subsequent 

 article. 



(D) Epidotization of the slate. 



In certain places in this district, the clay-slato is intensely 

 epidotized. This alteration is best observed in the environs of the 

 Mannen adit and near the western entrance of the Myojin tunnel, in 

 the southern part of the vein district under consideration. There, 

 the black slate is intricately penetrated by netted veins and veinlets 

 and irregular patches of bright green epidote, occasionally in as- 

 sociation with brick- red patches, thus giving rise to a confusedly 

 mottled appearance of black, green and red colours. 



The bright green patches and veinlets are composed of 

 epidote, clüorite and quartz, as is revealed under tiie microscope. 

 Epidote occurs in hypidiomorphic grains and idiomorphic prisms, 

 and shows distinct pleochroism, bright green to light yellow, and 

 bright speckled interference colours (PI. IL, Fig. 2). (,)uartz occurs 

 in xenomorphic grains and encloses epidote, slightly pleochroic green 

 chlorite in the form of flakes sometimes occurring in place of 

 quartz. 



The brick-red patches are composed of quartz full of hematite 

 dust, which is sometimes arranged in a radial manner. These 



