174 



ME. T. H. HOLLAND ON EOCK-SrECTMENS PROM KOEEA. 



refraction. Occasional flakes of these are of sufficiently larj^e 

 dimensions to determine the biaxial character of the crystals. 

 Similar brightly polarizing crystals have been frequently observed. 

 Dr. Hatch, for example, refers them to muscovite or kaolin *. 

 riagioclase is represented in the Soul granite by smaller crystals 

 exhibiting extinction -angles agreeing with those of oligoclase. 

 Albite and muscovite are found associated as secondary products, 

 infilling cracks in the rock. Most of the biotite originally existing 

 in the rock has been converted into chlorite, which exhibits the 

 pleochroism : E = yellowish-green, = dark green, and Avhich, when 

 treated with sulphuric acid, decomposes with the formation of 

 gelatinous silica. Of accessory minerals, magnetite occurs, and less 

 abundantly apatite. 



In the coarse-grained granite of Soul there occur veins of a much 

 finer-grained dark grey biotite-granite. Many of the crystals in 

 this rock seem to exhibit signs of growth after the formation of the 

 original crystal-outline (iig. 1). Much of the quartz, by intergrowth 



Pi^. 1. 



Crystal of ortlioclase showing secondary extension of the felspathic material, 

 irregularly intergrow ing with the neighbouring crystals. In biotite-granite 

 from the mountains north-west of Soul. 



■with the other crystals in the rock, produces a distinct pegmatitic 

 Btructure. Colourless acicular inclusions are common in the quartz. 

 Although the felspars, both orthoclastic and plagioclastic, are dis- 

 tinctly kaolinized, the biotite has undergone little or no apparent 

 alteration ; chlorite is present in very small quantities. 



Near the boundary between the provinces of Kyong-kwi Do and 

 Chhung-chhong Do, between Yukei and Eumsong, and for some 

 miles around the latter town, there is an extensive development of 



* ' The Spheroid-bearing Granite of Mullaghderg, Co. Donegal,' Quart. 

 Journ. Geol. Soc. vol. xliv. (1888) p. 550. 



