186 ME. T. H. HOLLAND ON KOCK-SPECIMENS FROM KOREA. 



porphyritic crystals and those of the smallest felspathic microliths 

 there is a curious correspondence, the larger crystals of the matrix 

 being found to correspond to the inner zones, which exhibit grada- 

 tions to anorthite. Zonal inclusions of the vitreous magma are 

 common ; and decomposition, with the formation of brightly polar- 

 izing flakes of a hydrous mica, muscovitc, zeolite, or kaolin, has 

 frequently destroyed the centres, or extended along fracture -cracks 

 in these crystals. 



Angite occurs in very large and almost colourless crystals, which 

 have suffered from incipient nralitization and separation of dusty 

 magnetite, together with the formation of chlorite, occasionally 

 vermicular, and secondary quartz in the cavities. 



In the matrix of the rock there are small fibrous hornblende- 

 crystals interspersed with cubic granules of magnetite. Epidote 

 occasionally accompanies other secondary minerals in the cavities. 

 It is impossible to form any reliable estimate as to the amount of 

 glass in the rock after its primary consolidation. 



A further stage in the decomposition of the Korean basic rocks is 

 exemplified in a specimen from the hills behind the Fusan settle- 

 ment, in the south-east of the peninsula. The porphyritic plagio- 

 clase-felspars, which are exceedingly numerous, have been almost 

 completely kaolinized, and a considerable amount of epidote formed 

 in granular crystals and radiating branches, together with chlorite 

 and the usual green products of an altered basic magma. There 

 are irregular straw-coloured patches of material, in many respects 

 serpentinous in appearance. Mr. Rutley mentions the occurrence 

 of a somewhat similar substance in the augite-andesites of St. 

 Minver, Cornwall*. 



The original ferro-magnesian silicates have been utterly destroyed. 

 Magnetite is plentifully scattered in small crystals. The specific 

 gravity of the specimens in Mr, Gowland's collection averages 2-78. 



A compact dark green rock from the Mungyong pass contains a 

 large amount of calcite, which effervesces with cold acids. The 

 specific gravity of the rock is 2-815. The felspars are seen, under 

 the microscope, to be converted completely into zeolitic products, 

 which give brilliant aggregate polarization-colours. Small granular 

 crystals of augite, showing the usual twin-phenomena and frequent 

 zoning, occur in great abundance scattered through the section. In 

 one section, two large quartzes, with the usual bands of inclusions, 

 have evidently been entrapped in the rock and partially fused. 

 Around each of the crystals, which are situated very close to one 

 another, there is an inner zone of brown, felsitic material not 

 unlike the matrix in many of the acid felsites, and it seems in this 

 case to have been produced by the fusion of the quartz with the 

 more basic matrix in which it occurred as a foreign inclusion. 

 Outside the felsitic zone there occurs a zone of granular crystals, 



* ' On some Eruptive Rocks from the neighbourhood of St. Minver, Cornwall,' 

 Quart. Journ. Geol. Soc. vol. xlii. (188(5) p. 393. Mr. Rutley (footnote, ibid. 

 p. 393) quotes Prof. Bouney's opinion as to the palagonitic nature of some of 

 tbe yellow patches. 



