GEOLOGY OP KOREA 73 



Middle Daido Formation (Middle ? Jurassic) 



Relation unhnoion 

 LoAver Keisho Formation (Upper Jurassic) 



Apparent conformitii 

 Upper Keisho Formation, Upper Daido Formation, etc. 

 (Earlier Cretaceous) 



Unconformity hy Denudation 

 Fuldvokuji Formation (Cretaceous ?) 



Unconformity of dip 

 Tertiary 



Palaeogene 



Unconformity of dip 

 Neogene 



Unconformity hy denudation 

 Quaternary 



Pleistocene (?) 



Unconformity hy denudation 

 Eecent 



Pre-Cambrian Sedimentaries :— The Pre-Cambrian sedimentaries 

 are metamorphosed in various degrees ; those intensely metamorphosed 

 being biotite-gneiss, calc-silicate bornfels, mica-shist, amphibolite, 

 pyroxene rock, crystalline limestone, quartzite, etc., those less 

 metamorphosed being phyllite, limestone, graphite-schist, etc. The 

 accompanying eruptives are gabbro, nepheline-syenite, serpentine, diorite, 

 etc. Mica, talc, and graphite among the non-metallic minerals, and 

 galena, zincblende and iron ores among the metallic are important 

 in this formation. 



Pre-Cambrian Gray Gneisses:— The gneisses are various in 

 composition and structure, the typical or.e being banded, fluidal or 

 schistose in structure and made up essentially of dark gray feldspar, 

 dark bluish quartz, and biotite, often of a golden colour, besides acces- 

 sory cordierite and garnet, both often present in abundance. They 

 grade into granite or augen-gneiss often called the Gray Granite- 

 Gneiss. The gi'ay gneisses are commonly rich in xenoliths of the 

 Pre-Cambrian sedimentaries, and the marginal })ortion of the xenoliths 

 is assimilated by, and ])asses into, the host. The gneisses occur in 

 general as batholiths or stocks in the Pre-Cambrian sedimentaries, and 

 their genesis is considered to be largely due to the assimilation of 



