106 B. KOTO 



imperfectly developed than in the crystals of eruptive rocks. The 

 mineral shows the dichroism ; cj = black, e = violet-brown. The 

 crystals are by no means pure; sagenitic needles, knee-shaped and heart- 

 shaped twins of rutile together with crystals of zircon occur imbedded 

 in them. The tourmaline itself is an unexpected guest in this chlorite- 

 amphibolite, and it is even more striking to find that rutile and zircon 

 which usually belong to the early generation in the order of crystal- 

 lization, occur exclusively confined in this tourmaline of an apparently 

 secondary origin. The tourmaline characterizes the rocks of the 

 Middle Sambagawan and its true home is, as has been already men- 

 tioned, the graphite-sericite schist ; but it is absent in the Upper as 

 well as in the Lower series. 



The compact variety of the chlorite- am phibolite is also exten- 

 sively developed in the Dözan-gawa near the Besshi mine in lyo, 

 Island of Sikoku. 



(d) The Upper Division. 



Epidote-sericite-gneiss. 



The Upper Sambagawan is not so extensively distributed as the 

 two preceeding étages, and so far as the writer is aware at present, 

 it is mainly confined to the southern side of the Arakawa river. 



The rocks belonging to this division overlie directly and con- 

 formably the hlacJc and green schists of the middle division, some- 

 times alternating with the non-spotted graphite-schist in its lower 

 horizon. The characteristic feature of the epidote-sericite-gneisses 

 with their various modifications which constitute the Upper Samba- 

 gawan, is a more or less platy structure with an uneven surface on a 

 cleaved specimen. There seems to exist some regularity in their 

 structural modifications ; for the lower horizon consists of a thick- 



