THE ARCHJEAX FORMATION OF THE ABUKUMA PLATEAU. 239 



tions. This lieino' the case, the fehlspar lias become encircled by quartz.^ 

 and this, as I have already stated, may distinctlv be seen in hand- 

 specimens even witli the unaided eye, altliono-li the sabsümce of the 

 feldspar has evidently snifered o-reat contortion, as may be inferred 

 from tlie bending- of the polysynthetic laniellge. 



Tlie nnhvinned, simple feldspar, a product of the second g-enera- 

 tion of the s;une mineral, has a habitus akin to that of tlie o-ranitic 

 quartz, having filled up the spaces l)etween the lamellated plao-ioclase, 

 hornblende, and biotite, and consequently imbedding the aboxe-men- 

 tioned minerals. It is highly probable that the ophitic feldspar, if I 

 may be a. I lowed to use this ex]3ression by analogy with the (jphitic 

 augite in diabases, is monosymmetric ; for, no polvsynthetic twi li- 

 nings have heretofore been observed in it. Tliis feldspar is a far later 

 pr(^duct of crystallization of the granitic magma, but its formation 

 took place slightly earlier or almost cotem])oraneouslv with that (^f 

 quartz, a.hhough no micropegmatitic structure has been produced. The 

 boundary between the later feldspar and tiie quartz is the most ir- 

 regular possible, indicating that they have consolidated not far from 

 each other in the order of crystallization. The later feldspar has not 

 suffered granulation, the (|uartz, on the contrarv, has been reduced to a 

 mosaic mixture. 



d) Schistose Vqndote-Granite. 



In macrosco])ic a|)])earance it differs from the ])receding bv its 

 dark shade, owing to the general distributiiMi tlirough it of chloritic 

 matters, and also to the presence of green patches of epi<lote. Its 

 structure is granulo-lamellar, nearly approacliing that of tlie plane- 



1 This peculiar structure seems by no means to be of rare occurrencp. Mr. T'eall, while 

 speaking of the granite from St. Davids, which has given rise to a good deal of discussion, 

 incidentally makes the following statements: The relation of the quartz to the feldspar in thi'^ 

 rock is interestinçi. Sometimes the two minerals occur in irregular grains, at other times the feldspar 

 plays the rôle of matrix to the quartz,... British Petrography, p. 318. 



