()4 ART. 2. — KOTO : 



nevaditic, rapakiwi-likc crystal-porphyry is found, composed of 

 feldspar and riuartz with an interstitial gronndmass of raicrogra- 

 iiitic aiiureo-ate, hesides blnisli-û,Teeii needles of hornblende and 

 brown crystals of titanite. Some of tlie idiomorphic white plagio- 

 claso crystals (1-2^- cm) are inclosed in shells'' of flesh-colored 

 orfchoclase (the reverse of the Finnisli rapakiwi), and tlie (jnartz 

 (1 cm) is round, sometimes liipyramidal ; — these two components 

 make up the greater part of the Inilk. The rock is a variety of 

 (piartz-masanite, and like the Finnish rapakiwi I assume it to be 

 a species of granite-porphyry of wliich the oft-mentioned masanites 

 are the representatives in Korea. Like its Finnish lelative it 

 may be used for decorative purposes ; but the feldspar and 

 quartz easily weather off, leaving hollows Itehind them, thus 

 preventing its extensive employment. 



This remarkable quartz-masanite extends as far as Yöng-san- 

 pho near Na-jiju, the limit of junk-navigation in tlie Yöufi-san-ganc/ 

 river, where appears a greenish porphyrite with plagioclase- 

 plienocrysts. It has a microfelsitic gronndmass, sometimes with 

 fluidal structure. ?)iotite is seen in the gronndmass. It is of a 

 uniqne t3'pe and proliably represents the marginal facies of the 

 preceding rock. 



Claystone-porphyry is found not far from tlie locality where 

 tlie preceding rock is found much decomposed. 



1) A I'lea vage- piece, which is split off from the common fnce (001) of the feidspar-pheno- 

 cryst, shows straight extinction in the lateruily attached flesh-colored, simple orihodafie, while it 

 extingiiishes light at about ±1° in the p;ily synthetically-twinned, white central portion. The latter 

 may be oligoclase, albite-oligoclasa or andesine, though it could not be decided to which variety 

 it really belongs from the examination of the basal section alone. Theface)>f basal cleavage of the 

 central portion exhibits macroscopic'dly the fine'striations which are characteristic of a plagiodase. 



As the shell of the orthoclase can ba easily detached from the rest, a section is made paral- 

 lel to (010) o£ the white, central p )rtion, and it shows under the microscope the extinction of 

 -f 15° 20' with reference to th3 edge P/M towards an obtuse angle, thus proving the nature of 

 the central part to be that of nUnte-oHgoclasc with the composition of Abai Alli)- 



