184 ART. 2. — B. KOTO: 



VI. The Felsophyre and its Allies 



We now come to deal with one of the many obscure prob- 

 lems in Korean geology — the problem with which we have 

 also been confronted in Japan, though no one has ever attempted 

 to solve it. It is the question of felsophyre, which is not only 

 represented by multifarious modifications, but also occurs in 

 close association with green porphyrite which has apparently no 

 genetical relation with the felsophyre. I have already mentioned 

 the quartziferous ^-^ fusion-breccia in connection with porphy- 

 rite, and also that the green breccia cannot be easily distinguish- 

 ed from the breccia derived from felsophyre "\ At any rate the 

 rather basic porphyrite and the highly acidic felsophyre, though 

 seemingly diametrically opposed, occur in close connection, and 

 the latter, so far as my observation goes, always underlies the 

 former ; but in time relation they are not far from one anotlier. 

 To explain the genesis of the two eflusives, petrologists are in 

 the habit of invoking the aid of magmatic difierentiation which is, 

 however, not easy to conceive in the wide distribution in 

 Korea of the complementary rocks in a comagmatic region. The 

 writer apprehends that the same difficulty about the porphyrite 

 will confront geologists outside the peninsular area, especially in 

 Japan and North China, and even in Borneo ''\ 



Another question presents itself to my mind, and this is 

 that the eff'Qsive felsophyre, according to my observations in the 

 field ^\ imperceptibly merges into normal quartzporphyry which in 

 turn grades into rhyolitic and nevaditic varieties, and then into 



1) See ante, footnote, page 44. 2) See ante, footnote, page 19, and footnote, page 98. 



3) Easton : ' Geologie eines Theiles von West Borneo.' Jaarloeh van het Mijninesen in 

 M iederlandsch Oost-îndië, Batavia, 1904. 



4) See ante, footnote, page 98. 



I 



