188 MR. T. n. HOLLAND O'S KOCK-SPECIMENS FROM KOREA. 



norite *, whilst the same thing has been observed by other authors, 

 recently by G. H. Williams in a hypersthene-gabbio of Balti- 

 more t. Large crystals of apatite occur, both in the matrix 

 and included in other minerals. The groundmass of the rock con- 

 sists of a plexus of colourless felspar-raicroliths, brown and green 

 hornblende, granules of magnetite, and interstitial glass, forming 

 the " hyalopilitic " structure of Kosenbusch. Secondary quartz, as 

 granular crystals, fills in the cavities. 



Some of the extremes of alteration of this class of rocks occur near 

 Fusan and Chhungdo. Nests of epidote, quartz, actinolitic horn- 

 blende, and magnetite weather out on the exposed surfaces as 

 knobby projections. In the specimens obtained from Chhungdo, 

 chlorite and epidote almost solely constitute the decomposition- 

 products. 



lu Kyong-sang Do especially, rocks of the foregoing types are 

 extremely common, and many of them from different localities have 

 been described by Prof. Roth, in the memoir so frequently referred 

 to, as diabase and diabase-porphyry, several also containing calcite. 

 Capt. Basil Hall mentions the occurrence on an island on the west 

 coast, in lat. 37° 45' N., of a " dark-olive, steatitic rock, containing 

 fragments of granular marble " X- 



The alteration of the felspar and other constituents into epidote 

 sometimes presents a different phase from that described above, in a 

 general formation of innumerable, disseminated, colourless plates 

 or granules of the mineral, either scattered loosely or gathered into 

 ill-defined aggregates. Patches of granular magnetite occur, 

 perhaps as relics of former ferro-magnesian silicates ; whilst secon- 

 dary quartz fills up the cracks and cavities. Some of the plagio- 

 clases still retain faint traces of twiuning-phenomena between the 

 granules of the epidote. Examples exhibiting these structures 

 occur in the hills on the east of Pumasa, about 21 U north of Tong- 

 nai, in the province of Kyong-sang. A specimen collected by Mr. 

 Gowland is dark-green in hand-specimen, and has a specific gravity 

 of 3 03. 



IV. Metamorphio Rocks. 



The most extensively developed amongst the Korean rocks are 

 the crystalline schists of probably Archaean age. Prom Von Tticht- 

 hofen's descriptions, we learn that this same group is most con- 

 spicuous also in the northern provinces of China, exhibiting — in 

 the province of Shantung — a general S.W.-N.E. strike §. 



Dr. Gottsche recognizes in Korea two divisions of these rocks : — 

 (1) A lower group of gneisses and mica-schists (Gneiss-Glimmer- 

 scliiefergruppe), with a general strike of S.W. and N.E., as 

 shown in the rocks near Kwisan, Chhung-chong Do, and between 



* Quart. Journ. Geol. Soc. vol. xlv. (1889) p. 343. 



t ' The Gabbros and associated Hornblende-rocks of Baltimore,' Bull. U.S. 

 Geol. Surv. no. 28, p. 21. 



+ Op. cit. Appendix, p. cxxiv. 



§ ' China,' vol. ii. pp. 221 and 706. 



