MR. T. n. HOLLAND ON ROCK-SPECIMENS FROM KOREA. 193 



places, conglomerato with well-rounded pebbles. At Iiidong these 

 beds have a dip varyiiipj from 15'^ to 20° S.K. ; and they occur not 

 far from localities in which l)r. Gottsclie collected specimens of pro- 

 bable Carbaniferous age *. Sections of one of these grits show it 

 to bo composed of sub-angular fragments of quartzite, schist, ortho- 

 clase- and pliigioclase-felspars, micrographic granite, occasional 

 bundles of mica, and chlorite. The grains are generally stained 

 with iron oxides, which latter are also deposited in the cavities. 

 The most interesting feature presented by these specimens is the 

 frequent occurrence of quartz-grains which have undergone secon- 

 dary growth. Hounded grains, darkened by inclusions, are sur- 

 rounded by borders of clear transparent quartz, that have grown 

 out to fit and interlock with neighbouring grains, whilst each border 

 is in optical continuity with its turbid nucleus. In one case, 

 which I have figured, traces of the crystalline faces, formed as free 

 surfaces during the secondary growth of the crystals, are seen as 

 parallel lines in the section (tig. 5). In the hand-specimen the 



Fig. 5. 



Secondary growth of quartz around a sand-grain. Minute inclusions show 

 parallel liueis of growth of the cryotalline form. In grit from Indong, 

 Kyong-sang Do. 



faces of the crystals thus formed are recognized by the way in 

 which they reflect the light from the plane-surfaces, like the so- 

 called " crystalline sands" which were shown by Dr. Sorby, in 1880, 

 to be produced in the same way by the secondary growth of quartz 

 upon sand-grains which were fragments of original quartz-crystals f. 

 The same thing has been shown by Mr. A. A. Young J, Dr. 11. D. 



* Op. c^Y. p. 807. 



t Quart. Journ. Geol. Soc, Pres. Addr., vol. xxxvi. (1880). 



I Amer. Jouru. Sci. 3rd ser. vol. xxiii. (1881) p. 207, and vol. xxiv. p. 47. 



