JOURNEYS THROUGH KOREA. 13 



flecks of feldspar which can oulj be recognized by reflected light. 

 Despite the fresh appearance, the rock under the microscopa is seen 

 to be very much altered. The original ferro-raagnesian nüüeral or 

 minerals have been entirely altered into epidote-grains ; but the silicate- 

 mineral in question was in all probability an augite. The structure of 

 the rock is pilotaxitic; the ground mass is made up of the lath-shaped, 

 twinned feldspar together Avith an interstitial, amorphous substance in 

 which are imljedded the phenocrysts of plagioclase. The rock is 

 probably an auglte-pœylnjrite. 



(2) The second is also a dark greenish-gray, compact rock with 

 angular fecks. Under the microscopo, it is seen to be composed of 

 angular crystals of plagioclase imbedded in the matrix Avhicli is made 

 up of polarizing particles together with crystals of magnetite and 

 fiue grains of epidote. The striped feldspar is partly epidotized, 

 forming clusters with regenerated plagioclase. The rock seems to be 

 a comf)act porplajrlte-tuff. 



(3) The third has a greenish-blue, compact flinty structure Avith 

 conchoidal fracture. It might easily be taken for a green jasper. 

 The mass consists microscopically of fragments of plagioclase and 

 round chalcedonic patches, a leucoxene-like substance and minute 

 glittering particles, intermixed with amorphous dust. It may be an 

 indurated porphyrite-tuf. 



Various modifications of dark-grayisb, compact augite-porphy- 

 rite together with tlieii\ derivatives, of the three types of which a 

 brief description has just been giveu, build up not only Chybl-hjmg- 

 do ^^ and outlying small island of I'ong-päik-syöm '\ but also a not- 

 inconsiderable portion of the south-eastern province of Ku'ông-sang. 



1) C. Gottsclie mentioned felsite-porphyry from Deer Island, though it is not represented 

 in my specimens ; but the possibility of its occurrence m.iy not be denied, for the same kind 

 of rock is found in many localities in the South Korean Archipelago, belonging to the forma- 

 tion in question. C. Gottsche : ' Ueber Land und Leute in Korea.' Verharidl. d. Gesell, f. 

 Erdkunde, S. 248. 188C. Berlin. 



2) ^ m m 



