190 ABT. 2. — B. KOTÔ:" 



writer to a whitish, earthy tuff-Uke rock cleaving into imperfect 

 tablets. The locality is the hill-neck Pam-chhi '\ south of Masan- 

 i:lio. Microscopically it is made up of interlocking aggregates of 

 quaitz and orthoclase of equidimensional grains and of the same 

 orientation, forming the so-called implication-structure. 



5. Common quartz -porphyry with a few phenocrysts of 

 quartz and orthoclase in a microgranitic groundmass is rare in 

 Korea, and was noticed by the writer only on the west of Chin- 

 häi. With this and the two following are the marginal fades 

 of neogranites. 



6. Masanite. — This is a buff-coloured, inequigranular rock 

 of the aspect of a fine granite on one side and of a quartz-por- 

 phyry on the other. Unlike aplite it easily falls to weathering 

 due to the loose aggregation of the quartz and orthoclase, pro- 

 ducing thereby an appearance of pumice both in colour and 

 texture. Besides, the phenocrysts of plagioclase weather away 

 leaving hollows behind them ; but the patches of quartz resist 

 atmospheric decomposition. 



The main bulk of masanite is built up of quartz and ortho- 

 clase which are equant, polyhedral and ec^uiforra, and the struc- 

 ture is interlocked or implicated. The quartz, however, shows 

 optical continuity extending to several grains so that the mineral 

 must be considered as plate in which orthoclase is imbedded. 

 The rock therefore has, so to speak, the antipegmatitic and 

 not the pegmatitic structure, for in tlie latter orthoclase serves 

 as the base. 



Another peculiar feature is the exclusively plagioclastic 

 nature of the zonal-structured feldspar-phenocryst witli indefinite 



1} See ante, puge 26. 



