154 Ar.T. 2. — B. KOTO: 



[ft. Felsophyre 

 ^'I. Felsophyre nnd its alliesii. Masanite. 



. Neoîïi'aiiite. 

 c. Grano-masauite. 



VII. Tertiaiy forinatiou. 



VIII. Diluvium and younger effusive«. 



IX. Alluvium. 



/. Tlie (Basal Gneiss 



I. a. The oldest known rock of the region is the sedi- 

 gneiss found exposed at a point about 4 bn from Pong-gol^^ at 

 the east foot of the Hoang-tai-chhi pass, west of Chin-jyu '\ It 

 underhes the basal muscovite sandstone of the Lower Kyöng-sang 

 Formation. The Pong-g'ôi gneiss ^^ occurs, so far as I have seen, 

 in a small strip (the strike N. — S., the dip E.) along the east 

 margin of the great granitic embossment of the Chirl-san massif. 

 The gneiss must have had in some remote aeon an extent of 

 continental magnitude, stretching eastwards even to Japan ; but 

 it was depressed and shattered, and is miderlaid by the Mesozoic 

 Kyöng-sang Formation, or otherwise assimilated by a hot bath of 

 magma in the zone (^f rock-flowage, and now it reappears as 

 small laccoliths in the form of granite through the Mesozoic, as 

 may be seen on the geologic map of south-east Kyöng-sang- 

 Do. 



The Pong-g'ôl gneiss is a light-brown, psammitic-looking rock, 

 consisting of quartz, ortlioclase, plagioclasc, and biotite with the 

 honey-comb texture characteristic of sedi-gneiss. It is variously 

 injected and interleaved, broken and healed by coarse veinlets of 

 granodioritic material consisting of hornblende, plagioclase, ortho- 



1) HI }^ or Tong-gyoi. 2) ^ 'Hi ^ee ante, piige 33. 3) See footnote, page 37, 



