246 ^ KOTÖ. 



however, not wanting, und s^Aarnl!>; of them cross« the rock vertical 

 ]y to its bedding. 



The quartz contains, besides, as enclosures, almost colourless 

 dodecahedrons of garnet, needles of zircon, and deep, reddish- 

 brown flakes of biotite — all making the quartz, between crossed 

 niçois, a])] »ear like a s])ongy mass. There are also fine, dark or 

 brown needles, sometiiues disjointed, shc^oting in various directions, 

 similar to those of the quartz in tonalité, which are so frequently 

 described, but whose natiu-e is so little known. i'he quartz is. as 

 usual, intensely chromatic, wheu viewed between cro.^sed niçois ; but 

 not all ihe quartzes found in this rock beha\'e in like manner. The 

 one which has been already granulated, displays vivid chromatic 

 colours ; while those which are still under high tension sho^v only a 

 weak grev tinge, and at the same time undulatory extinctions whi'-h 

 gradually sweep over the section one after another as is rotated. The 

 crystaUization of the silic;i must be of a comparatively recent date, as 

 may be seen from a grea.t number of ])re-existing miricrals contain- 

 ed in the substance of the quartz. 



Still later in its crystallization, or nearly cotem])oraneous with 

 that of quartz is the feldspar which, as I have already stated, makes 

 onlv a small fraction of the whole rock which not infrequently passes 

 locallv into a tvpical mica-schist. There are, however, other cases 

 in which Ihe rock makes transition in another direction, 1)y taking up 

 a large quantitv of both monoclinic aiid ti-iclinic feldspars in becom- 

 irjo- a tvi)ical ü'neiss. Generally s]>eakinü', the distribution of the 

 quartzose and feldspathic comj»onents in tlie rock are very fluctuating. 

 One portion may be built up only of Cjuartz, while the other will be 

 highly feldspathic, so that in a coarse variety found near Daibara in 

 Shimo-matsukawa, any one may name one portion of the rock a mica- 

 schist, while the other may be reasonably taken for a typical gneiss ; 



