MR. T. n. HOLLAND OX ROCK-SPECIMENS PROM KOREA. 173 



III. Igneous Rocks. 



Dr. Gottscho, in classifying the specimens lie obtained from 

 Korea, divided the igneous rocks into an older eruptive series 

 {(iltere Eruptivcjesleine) and a younger eruptive series {junyere 

 Ernptivgesteitie). lu the former group he includes granite, granite- 

 porphyry, felsite-porphyry, diorite, hornblende-porphyrite, gabbro, 

 and diabase ; whilst basalts and dolerites are the only Korean 

 igneous rocks which are not, according to Dr. Gottsche, of pre- 

 Tertiary age. As it is impossible, in the central and southern 

 provinces, to do more than prove that the eruptive rocks are of a 

 later date than the crystalline schists, I shall classify the rocks only 

 with reference to their structure and composition. 



There is abundant evidence of former igneous action, both plutonic 

 and volcanic, in this country as well as in the neighbouring 

 parts of China, described by Von Kichthofen ; but there is no 

 evidence of present volcanic activity, nor is there any record 

 of earthquake-action within the memory of man. The only 

 manifestations of the activity of internal forces consist in a few hot 

 springs in diifercnt parts of the country. Dr. Gottsche mentions 

 the occurrence of such springs, having a temperature of 76^ C, near 

 Tongnai, Kyong-sang Do ; and in the north at Tamni, north of 

 Unsan, in Phyong-an Do, having a temperature of 45° C* Mr. 

 Gowland found a hot spring at Brambe near the base, on the north- 

 west side, of the Mungyong pass. The water of this spring had a 

 temperature of 105° F. (45°-5 C.) in the bath ; it was perfectly 

 clear and transparent; without action on litmus, quite devoid of 

 taste or smell, and leaving no deposit. 



(1) Acid Eruptive Rocks. 

 a. Plutonic, 



Of the eruptive rocks, granite seems to be by far the most 

 abundant in the southern provinces, forming most of the principal 

 hills and exhibiting its characteristic weathering on the craggy 

 summits. 



In the mountains to the north and west of Soul, curiously 

 weathered crags of a coarse-grained granite rise to a height of 2000 

 feet. A specimen of this rock in Mr. Gowland's collection has a 

 specific gravity of 2-613. Under the microscope the large grains of 

 quartz are seen to contain the usual bands of secondary inclusions. 

 In places the quartz itself is secondary, and is seen to encroach on 

 a decomposing orthoclase, sometimes retaining the kaolinized pro- 

 ducts, which show the old line of demarcation between the crystals. 

 Vermicular chlorite is occasionally included. Orthoclase occurs in 

 large flesh-coloured crystals, frequently kaolinized in the centres. 

 Decomposition has given rise to the secondary formation of minute 

 nests of a colourless, micaceous mineral, possessing a high double 



* Op. cit. p. 862. 

 Q.J.G.S. No. 186. N 



