THE ARCHAWX FORMATION OF THE ABUKUMA PLATEAU. 223 



of a dioritic s^^enite. The colour of the quartz is light -grey, and 

 when it contains abiindancs of liqnid-inchisioiis, and also stiff, 

 bent, and broken trichites, it becomes more or less bluish in shade. 

 These trichitic bodies come indifferently in quartzes of the granite- 

 rnass, and in the veinlets which variously traverse the quartz. 



Notwithstanding the scarcity of macroscopic quartz, it is largely 

 represented microscopically in the rock, and forms, with micro- 

 cline or pJauiijclase, a fine aofOTeo-ate between the larwr individuals <jf 

 feldspar, hence the mortar-structure of Tornebohm. Under polar- 

 ized light between cr<jssed Niçois, the variously coloured mosaics consist 

 partly of the intergrowth of quartz and feldspar, radially arranged 

 aroiuid the feldspar individuals, forming a sort of delicate fringe, 

 and bringing about, in consequence, the pegmato|>hyritic' structm'e. 

 The latter is chiefly confined to the fine-grained variety, containing 

 richly zoned feldspar, but having oidy a small quantity of quartz-grains. 

 The liquid-inclusions are abundantly present, forming band-like 

 swarms, and the quartz containing them resembles a smoky quartz. 

 Hexagonal scales of biotite and rounded ci-ystals of zircon are also 

 found as enclosures. Undulatory extinctions and optically diverse 

 orientation of the grains show the rock to have iDeen sul)jected to great 

 pressure. It is remarkable to observe that where (piartz is plentiful, 

 striated feldspars with the cross-hatchini' structure are very abundant. 



Accessory components are apatite, zircon, and iron ores including 

 magnetite, titanic iron, and ])yrites. 



The apatite occurs as enclosures, especially in biotite and horn- 

 blende, and also as an independent ingredient. In the normal mass of 

 granite it is comparatively rare, but in the caught-up granite, as well as 

 in those of the contact cheeks of lamprophyres, tufts of apatite- needles 



1 Lossen, Vergleichende Studien lieber die Gesteine des S2}iemont!< und des Boseul/erf/s bei St. 

 Wendel u. verivandte Kruptirtypen aus der Zeit des llothlie<ienden. Jalirl). d. k()m;^l. preusa. geol. 

 Landesanstalt für 188'J. p. 270. 



