108 ART 2.— B. KOTO: 



tlie counterpart on the otlier extreme. There is, however, a 

 marked difference lietween the two leucocrates ; the anorthosite 

 has a marble structure with slight signs, if any, of the proto- 

 clastic, while the tourmaline rock is highly quartziferous, and is 

 made schistose by the mashing of the quartz, presenting thereby 

 a tj^pical cataclastic structiu'e. 



(I) The anorthosite, like Adam's Norian of Canada, is a gra^'isli- 

 "white, marble-like rock, being composed almost entirelj- of labradorite 

 with a small quantity of muscovite and quartz. A basal plato of a 

 cleavage-piece of the labradorite extinguishes light at — 17", and the 

 M face at 28° in the acute angle, — facts which imply the presence 

 of a labradorite of the composition o?>.,.. an--. Tlie anorthosite is seen 

 under the microscope to be built up of equiform (2 — .13 miii), equant 

 grains of coarse but distinctly pol3synthetic plagioclase twinned nfter 

 both the albite and the pericline laws. Characteristic black rods and 

 brown tal)lets of ilmenite are seen but rarely as enclosures. The rock 

 occurs, so far as I have seen, at two localities, viz., one near Ean 

 chhyöng^' at the east foot of the Cliiri-san, and the other near the 

 water-shed of the ChJujti-j^Jiiüig-jiyöng pass along the Seoul-Fusan rail- 

 way. One cannot fail to notice firstly, its jj»ec2«/{ar relation to the 

 adamellite since it occurs close-b}' and to the east of the exposures of 

 the adamellite ; and secondly, that anorthosite crops out aloi:g the 

 proto-axis of the granitoid lielt of South Korea. 



Like the classical anorthosite of the Laurentiau formation of 

 Canada, our rock is also the product of the magmatic diftbrentiation o 

 a gabbro magma. Near the ChIi]ju.-j>h/in(j-nyö)K/ already cited, Mr 

 Yabe took specimens of a typical hornblende-biotite-norito. This is 

 the only specimen of this rock ever seen by the writer in Korea. 

 Near San-chhyöng, the anorthosite contains greenish, fibrillated horn- 

 blende, which seems to have been derived from either hypersthene or 

 augite. In other Avords, it is a metagabbro. 



]) See ante, page 84. Here it is called pla'jiodasile . 



