JOURNEYS THROUGH KOREA. 



61 



fuj. 2) the back current was brushing along the northern margin. 

 As the l3ottom was shallow and the ferry narrow (1 km), the agitated 

 water was rushing over the rough bottom of volcanics at the 

 rate of 7 knots an hour, surging like rapids and roaring like a 

 storm ; hence the name M[/ö}if/-i/mi(/ or roaring sea. 



Chlii-do. ''—As to the geology of the island of Chin-do, I have ^^"^"^^ 

 no data upon wdiicli to base any conjectures. Its northern 

 portion at least seems to be built up of the same rock as tliat 

 of the opposite shore near Usu-i/öikj; but the greater portion of 

 the incised island is, according to Mr. F. Kobayashi, compos- 

 ed of brownish-red felsophyre which affords good soil for the 

 orowth of cotton for which the climate also is favorable. 

 While sailing along the coast, I saw at a distance at the southern 

 extremity of tlie headland of Tai-dun a gneissic (?) rock striking 

 north-south with a westerly dip. On the opposite point of 



formed behind the stream [which runs over a submarine ridge that traverses the narrows 

 from Shikoku to the island of Awaji]. These eddies exceed G jii in diameter and have a funnel- 

 shaped surface. If a boat be drawn into them, it is difficult for it to get out 



Comparing the phases of the tide just within and outside the channel, we observe that they 

 are nearly opposite to each other, a fact which at first sight appears paradoxical. The sea-level 

 of this i^art of the Seto-uchi is princiiially determined by the tide from the west. The tidal 

 wave of the Pacific enters the sea through the Bungo channel at the west end of the 

 island of Shikoki;, and proceeds eastwards towards the region under consideration, so that it 

 requires about 5 hours to travel th3 entire distance. Consequently the phase inside and 

 outside the channel of Naruto differs by about 6 hours, as actually observed, thereby producing 

 the difference of level of 1 to 1.5 m, as already stated. This is the cause of the eddying of 

 Naruto. 



When the current was rushing from the Pacific into the sea, an interesting phenomenon 

 was observed. As the current increased in velocity, a regular undulation of about 2.5 \n 

 became gradually conspicuous and attained a maximum amplitude of about 18 cm, and then 

 gradually decreased with the diminishing velocity of the current. The torrent of water rushing 

 from the Pacific into the channel excites a standing oscillation [due probably in part to the 

 submarine elevation which crosses Naruto and obstructs the current in its course] of water in the 

 neighborhood of the channel, just as a jet of air blown into the mouth of an organ-pipe 

 causes a standing oscillation of the air column in the pipe. ' Secondary Undulations of Oceanic 

 Tides ' by Messrs. Honda, Terada, Yoshida, and Ishitani. This Journal, Vt)l. XXV. p. 37. 1908. 



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