MR. T. n. HOLLAND OX R0CK-SPECDIEN3 FROM KOREA. 177 



meaus an unimportant constituent of the ori«2:inal rock. During the 

 changes which the rock has undergone, epidote has been formed, 

 biotite has been changed into chlorite, and a considerable develop- 

 ment of secondary (juartz occurs, infilling cavities produced by the 

 removal of decomposition-products from the felspars. Magnetite 

 occurs in cubic crystals. The rock has a specific gravity of 2-04. 

 Prof, lloth records the occurrence of a somewhat similar rock from 

 Puphyiing, Kyong-kwi Do, and another from Deer Island, off the 

 coast near Fusan *. 



Specimens of an acid volcanic rock were obtained by Mr. Gowland 

 south-east of Milyang, in the province of Kyong-sang. 



Porphyritic crystals of clear quartz and decomposed felspar are 

 seen embedded in a grey fiuxion-structured matrix. Occasional 

 fragments of green material, apparently caught up in the mass, are 

 found, on microscopic examination of the section, to be included 

 masses of altered rocks of the andesitic type. Many of the quartz- 

 crystals exhibit the geometrical outlines of idiomorphic crystals; 

 the majority, however, are so far corroded by the magma as to be 

 devoid of any trace of original form. The greatly kaolinized 

 felspars are seen in some cases to exhibit plagioclastic twinning. 

 An interesting example of the micrographic intergrowth of quartz 



Fig. 2. 



Micrographic intergrowlh of qu.artzand felspar, some of the latter being plagio- 

 clastic, and tbe whole considerably decomposed. The quartz has extended 

 its borders with an attempt at the formation of its normal, crystalline 

 outline; and has, by the dev^elopment of alternate forms, produced a rude 

 * babel ' quartz. In felsilic lava from Milyang, Zyong-sang Do. 



and felspar is represented in fig. 2, in which it will be seen that the 

 quartz has, by secondary growth, increased at the borders with an 



* Op. cit. p 87G. 



