THE ARCH^AX FORMATION OF THE ABUKUMA PLATEAU. 241 



e) Biotite-Graiiite. 



Thi8 is coarse and o-ranular and of a lighter shade, being made 

 up of a -flesh-red orthoclase, quartz, and a little biotite. Under the 

 niicroscope some muscovite may be seen, while this mineral is entirely 

 tvanting in the hornhlende-granite, alreadij described. The latli-shaped 

 feldspar with twinning lamellation extinguishes at small angles sym- 

 metrically Avith the twinning sutures, consequently this plagioclase 

 sliould be classed among the oligoclase series as in the other granites. 

 It is idiomorphic in comparison with the orthoclase, which usually 

 encloses it, and consequently the lamellated one must be the older. 

 The orthoclose is more or less kîiolinized, and its crystals are usually 

 twinned on the B;iveno type. The quartz has the same habitus as 

 that in the hornblende granites, and is ])Oor in liquid-inclusions. 

 The biotite is common ; zircon and the blot^d-red iron glance are found 

 as accessories. The rock occurs in good exposures at Kawa-uchi, 

 Naraha göri. 



The most interesting fact in connection with this granite of the 

 Abukuma ])lateau is the occurrence of black ixitches of the hornblende- 

 granite caught up and enclosed by the light-cohmred hiotite-granite. The 

 enclosed granite is really the thigments with sharp angular edges, 

 torn otf with great fjrce from a mass of completely consolidated rock 

 of older date. The size of the fragments varies from 5 to 15 cm. 

 New^ road-cuttino'8 and the bottom of rivulets ex])Ose the structure in 

 full detail. Looked at fi-om a distance, the rock appears like a coai-se 

 conglomerate or breccia, or a mass stained with gn^ss marks upon a 

 white ground. It is indeed a, breccia of effusive origin and primary, 

 the older black granite, bearing the hornblende, being ceuiented with a 

 matrix of the younger 5ioi/i6-granite, tlie latter differing from the first 

 only in the different development of ferro- magnesian silicate. The 

 granite enclosing the older fragments is wide-spread in the region 



