THE AROHiF.AX FORMATION OF THE ABUKUMA PLATEAU. 243 



others again are real ench^sures of either ([uartz or feldspar with other 

 optical orientation than the main mass, while the third are rather 

 laro'er patches of another kind of feldspar with systems of twinning- 

 striations nearly at right angles to those of the enclosing minerals. 

 The last have a, close similarity to that of the alhitized orthoclase of the 

 Socotra granite, as descril)ed and figured by Dr. Sauei-J from which, 

 however, thev diifer only in one particular that the changes which 

 the mineral has undergone are not in orthoclase. hut in the substance 

 of a striated feldspar. The orthoclase is romparatively free from these 

 ])atches of ])lagioclase, but full of irregular cracks. The quartz out- 

 weighs the striated and the non-striated feldspars, therefore this rock 

 nuist ])e of highly acid composition. Minute ci-ystals of apatite <are 

 abundant in quartz near the margin of biotite, being often dismember-: 

 ed and crooked ; the j)leochroic halos are obser\ed in biotite ; globular 

 o'rains of maofnetite are scattered tln'ouii'li the oeneral mass. Zircon 

 is also found in fine crystals in the condji nation of the fices of j: T, 

 andx Px , with indistinct terminations. 



The cnchm'à <iranittc patclics. — The ]>lagioclase is idiomorphic 

 with respect to that of the biotite-granite, and at the same time zonings 

 are beautifully developed in it, whidi are not found in that of normal 

 h(^rnblende-granite. At times its central portion is more or less 

 decom])Osed, and crystalloids of a bottle-green hornblende are scatter- 

 ed throughout that area (Fig. 7, V\. XXTH). The feldspar is on the 

 other hand fresh and intact in its outer, and the hornblendes within 

 the core were probably formed by contact metamorphism. Epidote- 

 grains of a tolerably large size occur enclosed in an ajiparently un- 

 changed feldspar. The epidote seems to be wanting in the biotite- 

 granite (intruding granite). Striated and non-striated feldspars oc- 

 cur in equal quantities, but their distribution in the rock-mass is not 



X Zeitschr. d. deutschen, geol. Gesellschaft, Vol. XL, p. 14G. 



