194 MR. T. H. HOLLAND ON EOCK-SPECIMENS FROM KOREA. 



Irving *, and Mr. Van Hise f to be the cause of the structure 

 of certain sandstones and quartzites in the United States. 



The peculiar effect produced by light reflected from the surfaces 

 of these small quartz-crystals, somewhat resembling minute frag- 

 ments of " Belleek " ware, might be due to the same cause which 

 produces the characteristic appearance of Professor Harkness's mine- 

 ral, cotterite :{:. 



YI. Summary. 



Although the southern half of Korea may be looked upon as a 

 distinctly hilly country, there are no mountains exceeding 3000 to 

 4000 feet in height ; and these are, for the most part, rounded 

 hummocks bounding rice-growing valleys and plains. 



The rocks building up these hills are chiefly members of the group 

 of crystalline schists and gneisses, with graphite, garnet, dichroite, 

 and fluor occurring in considerable abundance ; and the whole group 

 forms probably a part of the great mass of Archaean rocks of north- 

 eastern China, so well-known through the descriptions of Von 

 E-ichthofen. 



Stratified rocks of various kinds (shales, sandstones, grits, and 

 conglomerates) lie unconformably on the schists in the south-eastern 

 part of the peninsula, and are probably of Carboniferous age. 



Through the crystalline schists and stratified rocks various 

 igneous rocks have been erupted, and are now exposed as projecting 

 dykes, or, in large masses, as bare, rounded hills and mountains. 

 Amongst the results of igneous action granite is the most con- 

 spicuous rock. Eiotite- and muscovite-granites are most widely 

 distributed, and in places are cut by dykes of eurite (or " felstone ") 

 and veins of quartz and pegmatite. The more basic class of rocks 

 is represented by diorites, propylites, andesites, basalts, dolerites, 

 and gabbros (Prof. Roth). Interesting cases of the gradual passage 

 between the so-called intermediate and basic rocks are found, and 

 various stages in the devitrification and decomposition of andesitic 

 lavas are represented. 



There are now no active volcanoes, neither are there any known 

 records of the occurrence of earthquakes. The only manifestation 

 of the present activity of internal forces consists in the warm 

 springs occurring in various parts of the peninsula. 



There is a notable lack of mineral wealth in the southern part of 

 Korea. 



* Amer. Joum. Sci. 3rd ser. vol. xxv. (1883) p. 401. 

 t Bull. U.S. Geol. Surv. No. 8. 



I ' On Cotterite, a new variety of Quartz,' Mineralog. Mag. vol. ii. (1878 

 p. 82. 



