MR. T. n. HOLLAND ON ROCK-SrECIMENS FROM KOREA. 185 



Amongst the specimens collected by Mr. Gowland, one of the 

 freshest types of basaltic rock obtained was from a river-gorge near 

 Chhongdo, in the province of Kyong-sang, In the hand-specimen 

 the rock is a dark-green, compact variety, with an abundance of 

 long felspar-crystals arranged in approximately parallel directions. 

 The specific gravity of the rock is 2*81. 



The porphyritic felspars, judging from the angles of extinction 

 measured, have a composition approximating to that of bytownite. 

 They are well twinned, principally on the albite type, and contain 

 frequent inclusions of glass, especially in marginal zones. These 

 crystals are porphyritic also in the sense in which this term is 

 employed by llosenbusch. The early consolidation of these large 

 crystals of felspar is further indicated by the occasional occurrence 

 of specimens M-hich have been split asunder along the Gleitfldchen 

 and cleavage-planes, with intrusions of the matrix, which has either 

 crystallized out, like the general matrix of the rock, or consists 

 solely of augite, which hfis been partly changed into green fibrous 

 hornblende. 



The original ferro-magnesian silicate has been converted into the 

 various green decomposition-products. In some cases, this is dis- 

 tinctly serpentine, either alone or mixed with chlorite. Patches 

 of green fibrous hornblende, with its characteristic pleochroism, 

 occur with these green products. 



The constituents of the matrix have consolidated in the order 

 which they follow in the description : Magnetite occurs in well- 

 marked, cubic forms, seldom accompanied by titanoferrite. Small 

 lath-shaped crystals of plagioclase are abundant, both in binary 

 and in repeated twins, which, from their angle of extinction 

 are closely allied to lahradorite or andesine. Augite fills in the 

 intervening spaces, with the formation of the ophitic structure of 

 M. Michel-Levy on a small scale — the micro-ophitic structure 

 described and figured by Prof. Judd in certain basaltic lavas of 

 Mull *. The augite in the Chhongdo rock has partly changed into 

 uralitic hornblende. The occurrence of ophitic structure indicates 

 according to Prof. Judd, consolidation of the rock under condi- 

 tions of comparative quiescence ; hence in this rock the porphvritic 

 felspars must have acquired their approximately parallel directions 

 before complete consolidation, or before the rock assumed the quiet 

 conditions preparatory to solidification. As might be expected from 

 this, the microlithic felspars of the groundmass exhibit, with reo-ard 

 to direction, no such regularity of arrangement. 



A compact dark-green porphyritic basalt occurs S.E. of Milyang, 

 in Kyong-sang Do. The specific gravity of the rock is 2-80. 

 Under the microscope, plagioclase, augite, and magnetite are 

 porphyritically developed in a finely granulitic matrix. " Pro- 

 gressive " zones, due to changes in the chemical composition of the 

 crystallizing magma, not unfrequently characterize the plagioclastic 

 crystals. Eetween the extinction-angles of the outer zones of the 



* Quart. Journ. Geol. See. vol. xlii. (1886) p. 68, and pi. v. figs. 3, 5, & 7. 



