THE AROH^.AX FORMATTOX OF THE ABUKUMA PLATEAU. 225 



so-called aveiitiirine lustre. The other h'on ore, titanic irou, seems 

 to occur in the rcick, since its presence is iiidiciiterl l)y the formation of 

 leucoxene borders around the cores of ii'on. Zircon in grains and also in 

 crystals of the usual habitus is chiefly enclosed in the h«^rnl)lende and 

 biotife. 



Spliene is onlv observed in the hornblende-^'raiu'te from Xakii- 

 tani, near Tshikawa. Fluorite^ so common in granites, is wanting. 



'ilie colonrcd componrnts are represerited by biotite, as well as by 

 hornlilende, and form the characteristic, dark, confusedly fibrous 

 parts and flecks in the gneissose variety of the granites. In the striped 

 granite the mica and hornl)lende have the same orientation, and the 

 base of the l^iotite and tlie c-axis of the hornblende lie in the same 

 plane. Conseqnently the maximum-extinr-tion happens simultaneous- 

 ly in the two minerals, along the plane of the pressure-cleavage of the 

 rock. Apatite, zircon, and magnetite are fonnd as enclosures in the 

 mica, while the hornblende contains besides them crystals of biotite, 

 showing that the latter is of earlier generation than the former. 

 The usual chloritic material, resulting from the decomposition of horn- 

 blende is absent in the cases hitherto observed. The amphiljole is 

 remarkablv fresh. The biotite is, however, partially altered into green 

 lamelleö by the lileaching of that mineral, these changed bands being 

 interlaced with the fresh foliœ of the biorite ; and the secondary 

 epidote is aJso fonnd in the 1)leached parts. 



The biotite is by i'nv the most common of the two minerals; the 

 absolute quantity of it may, howeNcr, fluctuate within wide range. 

 The pleochroic halos usually so common in it are discerned here only 

 in a few cases. Observed from the base, it is of a dark-brown shade, 

 and sometimes so interisely coloured as to give the appearance of an 

 opaque body. It may at once be conjectured that the mineral is highly 

 ferriferous, and the result of an analysis made l)y Mr. Hida, of the 



