THE ARCHiEAX FORMATION OF THE ABUKUMA PLATEAU. 245 



YI. Petrography of the Takanuki Series. 

 A. Gneiss-Mica-Schists. 



This occurs in a tiilnüar form with the plane-parallel structure ; the 

 surface of a cleaved slab of this rock is entirely covered with aggregates 

 of biotite, while its transverse section is striped with black on a 

 yellowish- white ground. This peculiar appearance arises from the 

 interbanded zones of black mica in the quartz-feldspar layers ; the 

 general colour is light-grey with a slight tinge of yellow, being caused 

 by the pigment of the hydrous sesquioxide of iron that has infiltrated 

 every fissure in the quartz and feldspar. Where biotite forms a com- 

 ponent only in small quantities, this rock approaches both in ap]>ear- 

 ance and composition to a granulite. Of course, such a granulite 

 deviates in habitus from the typical one of the Mittelgebirge of Saxony, 

 in having a rather coarse-granular texture, and als(3 by the absence of the 

 so-called microperthite. Weathered exposures of this rock look not 

 unlike a disintegrating sandstone-mass. 



The prevalent component is quartz, and the rock may fitly be termed 

 a biotite-schist. The quartz abounds in liquid-inclusions with enclosed 

 bubbles which on warming soon disap[)ear fi'om sight, indicating the 

 presence of liquefied c<!rb(jnic acid. These liquid-inclusions form 

 chains, traversing different grains, irrespective of diverse crystal logra- 

 phic orientations, as is frequently mentioned in writings on crystalline 

 schists. This phenomenon Avould be best studied in a slice, cut 

 parallel to the plane of schistosity of a rock, brought from Shimo-Matsu- 

 kawa, near the village of Takanuki. Contrary to my expectations, 

 it was, however, not observed in a slice made at right angles to the 

 former section, a fact indicating that the rock had yielded to pressure, 

 in the direction parallel to the plane of schistosity, but not in that at 

 rig-ht angles to it. In individual grains, hquid-inclusions are, 



