ON T[It: SO-CALLED CRYSTALLINE SCHISTS OF CHICHIBU 117 



(g) The Middle Sambagawan. 



This division plays îiii important role among the Sambagawan 

 series, amounting to about 200 m. or -f^ of the whole thickness, made 

 up of alternate layers of the chlorite-amphibolite and graphite -sericite- 

 schist. The whole middle complex lies conformably upon the Lower 

 division, and occupies the greater part of the area of our geological 

 terrane. As a whole, the green schist predominates in the lower 

 horizon, while the black schist chiefly constitutes the liigher part ; 

 and both are directly overlaid by rocks of the Mikabu series, when 

 the Upper Sambagawan is wanting. 



The chlorite-amphibolite or spotted green schist is extremely 

 rich in the white "' eyes " of a scmssuntic felspar, which become more 

 clearly visible on a w^eathered surface ; but sometimes, nay, indeed 

 very frequently the fresh surface of a rather compact variety does 

 not show any sign of the presence of the "eyes"; and this is the 

 source of a lamentable confusion of this rock with the overlying 

 Mikabu rocks — both being habitually indiscriminately termed chlorite- 

 schist, although they are really separated by a wide stratigraphie gap. 

 This green, spotted schist not infrequently comes together with the 

 piedmontite-schist (i. g. in Todoroki near Obata, and Minano), and the 

 former is rather compact and less fissile than the spotted, black schist. 

 The graphite-schist becomes coarse-lameller (Oda and also in the neifj^h- 

 bourhood of Onisi) through the i)resence of the black " leather-bag- 

 shaped" crystals (ß(j. 6) of felspar ; and through weathering the rock 

 acquires a brown colour, presenting an aspect quite distinct from the 

 spotted graphite-schist. 



1. — Both the chlorite-amphibolite and graphite-schist occur in 

 an isolated district east of Ogawa, Avhere they overlie the piedmontite- 

 schist, and dip to the north-east, being directly covered on the north by 

 gray wacke-sandstone and in part by the Tertiary of the Ogawa basin. 



