92 B. KOTO 



in the lack of any special arrangement, from the other mineral com- 

 ponents. Optical anomalies are not observed in pure individuals. 



Some occurrences are particularly rich in Calcite in irregular 

 patches, occasionally, however, in the idiomorphic form of perfect 

 rhombohedral crystals. The latter case seems usually not common 

 in the gneiss of the Archaean group. Calcite-patches often contain 

 quartz- and felspar-grains. Traces of the rhombohedral cleavage 

 appear in bent and zigzag lines, partaking of the plicature of the 

 rock-mass itself. It is highly probable that the calcite in this rock is 

 of a primary nature. 



The opaque iron-glance and the blood-red iron-mica are constant 

 components in this rock as well as in those of the two upper divi- 

 sions. The opnque iron-oxide has a lamellar structure and exhibits 

 a bluish tinge on the smooth surface, when ol)served by reflected 

 lig-ht. Botli varieties of hematite are usually irreo-ular in their 

 distribution, being massed together in one part and remark ai)ly absent 

 in others, and, as has been already said, they are particularly rich 

 in the felspars and epidote. 



The rutih' is the most characteristic component of the Lower 

 Sambagawan Series. It occurs in both types of twins, the one is 

 heart-shaped, being composed of broad crystals, the other knee-shaped. 

 These sometimes occur in trilling according to Px and 3 Poo at the 

 same time. So far for the descriptiim of the component-minerals. 



The normal sericite-fichist has itself a special structure, being caused 

 by an alternation of the quartz-felspar mass with fine layers of sericite 

 too-ether with garnet, and ores of iron-oxides ; and as the consequence 

 of such an arrangement, the rock cleaves into thin plates. A good 

 exposure may be observed at the quarry in Sueno near Yorii. 



A peculiar structure has been observed in the course of the study, 



