MR. T. n. HOLLAND ON ROCK-SPECIMENS FROM KOREA. 189 



Kwachluin and Sciiil. (2) The upper p;roup of phyllites (Phi/Uit- 

 f/ri(ppe)^ with a p;oiieral N.W. and S. K. strike, and nortli-easlerly 

 dij), as shown in the chiastolite-shite of Miin<iyonjr and llainchhanf>-. 



The former jj^roup includes raica-schists and gneisses, hornblende-, 

 chlorite-, and talc-schists, crystalline limestones, dolomite, eklogite, 

 and micaceous iron-ore. The phyllite - group includes various 

 phyllite-, chiastolite-, quartz-, and graphite-schists, as well as 

 micaceous iron-ore. 



In the specimens of gneiss which I have examined, biotite is by 

 far the most abundant ferro-magnesian silicate ; but a gneiss with 

 two micas was obtained by Mr. Gowland between Yukei and Eum- 

 song, in Kyong-kwi Do. J)r. Gottsche moutions the occurrence of 

 muscovito as well as biotite in specimens obtained from Hatang- 

 gyom, south of Keumsan, in N. Chol-la Do *. 



The museovito-biotitt; gneiss in Mr. Gowland's collection exhibits 

 under the microscope the ordinary mineral constituents of a typical 

 granite, in which muscovite is in excess of biotite, and both of 

 which are curved and bent by the crushing to which the rock has 

 evidently been subjected. The biotite is changing in places into a 

 green, pleochroic form, which shows a deep grass-green, colour, with 

 rays vibrating parallel to the fibres, and pale straw-yellow, with 

 rays vibrating perpendicular to the basal cleavage. Bundles of the 

 colourless " biaxial " mica are sometimes interlaminated with the 

 brown, pleochroic variety. This interlamination evidently occurred 

 before the crumpling of the mica-bundles during the dynamic meta- 

 morphism which has brought the rock to its present condition. 

 Nests of colourless mica are common in the kaolinized felspars, and 

 in cracks, together with other secondary development of mineral 

 matter. 



The felspars, which are of both plagioclastic and orthoclastic 

 varieties, have been considerably kaolinized. Occasionally a. 

 peculiar intergrowth of two varieties gives rise to the structure to 

 which Becke, in 1882, gave the name " micro-perthitic " t. The 

 numerous quartz-crystals present invariably exhibit " undulose " 

 extinctions. Besides the ordinary bands of inclusions running 

 across the crystals, there is a frequent development, along planes, of 

 a series of communicating, irregularly shaped lacunae and canals. 

 The production of a graphic structure on a small scale results from 

 the frequent intergrowths of quartz and felspar. Apatite is present 

 as acicular crystals. The gneissose structure is quite apparent; 

 but the rock presents all the appearances of a simply crushed 

 granite. 



Evidence of more complete dynamic metamorphism is afforded in 

 various parts of the peninsula. A common type of gneiss may be 

 represented by specimens obtained near 8oul, and between that city 

 and Kwachhon towards the south-east. In these rocks we have 

 examples of a true Augen-gneiss. Under the microscope, quartz is 



* Op. cit. p. 802. 



t ' Die Gueicslurniation des niederosterreichischen Walclviertels,' Tsch. 

 Mill, und Petrogr. Mittbeil. vol.iv. (18&2; p. 107. 



Q.J.G.S. Xo. 180. 



