6 Vol. X LUI.. Art 5— T. Ki.tô: 



This district consists of sedimontaiy rocks of Paleozoic and 

 Mesozoic ages, together with igneous rocks such as diorites, por- 

 phyrites, andésites, liparitic rocks and others. 



(A) The Paleozoic Formation. 



The Paleozoic formation^) developed in this district consists 

 chiefly of slaty rocks with subordinate qnartzite, sandy rocks, and 

 schalstein in association witli diabase. The complex is highly 

 disturbed, but in general the strata strike N, 40--50'^ E. and dip 

 towards N.W. at an angle of 30 --50°. 



Chvj Slate. This forms the most important country rock of 

 the copper-tin veins of this district. Fresh slate, not influenced by 

 mineralizing solutions, is commonly rich in carbonaceous matter 

 and black in colour, hard and compact, and shows rather indistinct 

 cleavage. Under the microscope, the black slate is seen to consist 

 largely of an exceedingly fine textured base or paste, very diflicult 

 to resolve, in which fine grains of quartz and feldspar, flakes of 

 chlorite, etc. are imbedded. Carbonaceous matter is abundantly 

 scattered in dusty particles or in minute specks. Sometimes it is 

 silicified to a considerable extent and is penetrated by veinlets 

 consisting of quartz and epidote. This rock is well exposed in the 

 environs of the Shotoku adit, as well as near the western entrance 

 of the Myùjin tunnel, and in several other places. 



The slate is frequently altered to dark green rocks, particularly 

 in the environs of the Daisen vein. At first sight the altered slate 

 is scarcely recognizal)le, because the slaty cleavage has usually 

 disappeared, and the rock has lost its splintery nature and become 

 rather massive. The faint appearance of bedding in places is the 

 only remaining fleld evidence of tlie original character in some of 



1) So-cixUed " Cliichibu System." 



