106 ART 2.— B. KOTO: 



from tli8 xouomorpliic ortlioclase, wliicli has a rounded outline, is 

 often altered into muscovite, and occurs in the poikilitic fashion. 

 Tlie ortlioclase -xîrystallized earlier than the raicrocline, and is poorly 

 represented in the rocks of onr area. The xenomorphic raicrocline 

 often encloses smooth polygonal and sometimes drop-slifi-peä quartz of 

 the same orientation. This is a sort of intergrowth akin to graphic 

 granite. When the raicrocline and interstitial quartz come in direct 

 contact, the sutvu'e is that of irregular juxtaposition due to their simul- 

 taneous crystallization. 



Oligoclase of the dioritic habit is always idioraorphic and zonally 

 structured with the piuitified nucleus, and twinned after three laws. 

 The polysynthetic laraellation is fine, continuous and equidistant. As 

 it is not possible to get cleavage-pieces the determination of the plagio- 

 clase is of only approximate value. The symmetrical maximum angle 

 of extinction Avas maasured at al)Out 5°. The Becke method gave 

 the following result : 



(oya' (o<:ß' 



Tlie feldspar is therefore a basic oligoclase with the composition ab. 

 aui — ab. aUj. The size is usually small, and it is often surrounded by 

 a myrmekitic border. Accessories are common epidote, allanite, musco- 

 vite, titauite, garnet, sillimanite, zircon and apatite. Primary iron ores 

 are scanty. 



IV. h. M elan ocra te. — One of the striking features in the 

 gneissoid terrane is the occurrence of a long but appai'ently in- 

 terrupted belt of adamellite along the east margin of the So- 

 paik-san range from the southwest coast through tlie Iloang-tai- 

 chhl pass (p. 39), Tang-song (footnote p. 35), Scm-chhijony (p. 84) 

 as far as to Sang-jya at the northwest corner of Ky'ông-sang-Do. 

 It is undoubtedl}^ a basic marginal faciès of the light-colored, 

 acidic granitoid of the So-pàlk-san laccolith through which it liad 

 intruded before the complete solidification of the main mass. I 



