JOUENEYS THROUGH KOREA. 183 



the entire tract of the Strait of Tsuslnma including the coastal 

 regions on both sides, with the axis trending northeast and 

 southwest corresponding to that of the strait. It is obvious that 

 the Mesozoic mountains, situated between the Alpine ranges of the 

 So-pälk-san and Chii-goku, once connected the insular empire with 

 the continent. Since then, the intervening tract has been cut off 

 by the subsidence of the Mesozoic ground, and the isolated islands 

 of Tsushima bear witness to the great geographical revolution 

 that made Japan an island group. As to when the last diastro- 

 phic changes took place, I can only say that it was probably at 

 the end of the Tertiary, as may be surmised from the Tertiary 

 deposits which flank the coastal slope of the already uplifted Meso- 

 zoic mountains. The Mesozoic basin of the Tsushima area seems to 

 have been shallow on the Korean and deep on the Japanese side. 

 Much light will be thrown on this subject if, as Gottshe 

 has already attempted to do, the geology of Tsushima ^^ is work- 

 ed out in detail. The Tsushima area in my opinion forms a 

 geological unit, and the whole range of the Mesozoic group will 

 be embraced in the Kyöng-sang formation in the broad sense of 

 the term. 



1) Mr. Nasa visited the islands of Tsushima in 1891, and found an extensive development of 

 a complex of shale, slate and sandstone, which vividly impressed him with its close resemblance 

 X)etrograxDhically to those of the ]Mesozoic terrane of Kaga i^rovince. {Bulletin Imp. Geol. 

 Surv. [in JajDanese], No. 1., 1891.) 



Lately, Mr. Sato reconnoitred the islands and found alsa the shale and sandstone, the latter 

 calciferous and muscovitiferous. He divided the complex into two groups : the lower sometimes 

 becomes conglomeratic and has ipoor seams of anthracite (18-20 cm thick) with Ostrea ; the 

 upper is intercalated with sheets of quartzporphyry and porphyrite. The whole complex 

 is thrown into folds with the anticlinal axis trending from northeast to southwest with the 

 prevailing dip to the southeast, though the contrary was frequently observed. Sato likewise 

 assigns the age of the complex to the Mesozoic (Lias). {Explanatory Text to the Geologic Map 

 of Kamiagata, Tsushima Is. [in Japanese], 1908). To the writer, the Tsiishima Mesozoic seems 

 to have a closer affinity to that of the Japanese side than to that of the Korean. 



