188 ART. 2.— B. KOTÔ: 



2 c. Close by the Korean Cliarybdis is the small hill, Ok- 

 mai-san by name, noted for the material used in making the fine 

 cigarette boxes which we frequently find in shops in Seoul. It 

 is an unctuous, white claystone — the " ok- mai stone " ^\ It 

 consists of pure, amorphous clayey matter impregnated with 

 granules of hematite making carmine-red flecks in the rock. It 

 is probably a local sedimentation of decomposed felsophyre, later 

 subjected to post-volcanic action which produced the grannies of 

 hematite. The rock resembles lithologically as well as geolog- 

 ically the " mitsu-ish stone " of Bizen, Japan, where the rock 

 is now being extensively quarried for refractory bricks (p. 59). 



2 d. A spherulite-porphyry occurring near the eumnai of 

 Häi-nam. It is a hght-brown rock with abundant grains of 

 quartz set in the spherulitic gronndmass. Altered orthoclase and 

 biotite are also present. 



3. The crystal -porphyry typically exposed at Yu-dal-san 

 near the free port of Mok-plio, not to mention many others. It 

 is a grayish, coarse, nevaditic rock containing a few crystals of 

 biotite and flesh-coloured microcline, but a large quantity of cor- 

 roded grains and bipyramids of qaartz. The gronndmass is a 

 granulo-crystalline felsitic matrix. The microcline easily weathers 

 off leaving hollows behind it, giving it the rough aspect of rhyo- 

 lite for which it was formerly mistaken. 



A remarkable, nevaditic, rapakiwi-like "^ crystal-porphyry was 

 brought home by Mr. Inouyk from the mouth of the Y'&ng-san-gang 

 near Mok-pho. It is built up of crystals of oligoclase and quartz 

 with an interstitial gronndmass of microgranitic aggregate with 

 bluish-green needles of hornblende and crystals of titanite. 

 The white plagioclase (1-2^ cm) is enclosed in a shell of flesh- 



1) s JS ïi" or 3Î ^ :5 = '■'precious üower-stone." 2) See ante, page 64. 



