Okhotsk Sea. — In the northern part of the Okhotsk Sea the conti- 

 nental shelf is 50-100 metres deeper in comparison with other regions. 

 This fact suggests that there must have been a relative change in sea-level. 



2. Special Configuration 



A. Great Earthquakes and Submarine Configuration 



After the great earthquake of the South Sea at 4:.19 a.m., on the 

 21st December, 1945, the sea area of Kishu and Shikoku was deepened 

 about 1 metre in general. Also large-scale steep slopes were introduced 

 to the submarine configuration in the vicinit\' of the epicentre. 



B. Suhniarine Valleys 



There are many submarine valleys along the Japanese coasts. The 

 lower limit of the valleys extend beyond 1,000 metres depth, and the 

 upper limit (shallower) is cut deeply in the continental shelf. Some of 

 the valleys have their upper limit around 120 metres depth, while others 

 are even shallower, sounding only 20 metres depth. The valleys are 

 imbricate, with man\- branches (tributaries) cut into the continental 

 shelf. 



C. Ridges and Banks 



lAdSiy ridges and banks have been found to be distributed near the 

 continental shelf of the Japanese Islands. These ridges and banks 

 are arranged roughly parallel to the coast of the Japan Sea and are 

 provided with steep slopes with rather flat summits which measure 

 only 120-140 metres in depth ; these appear like tilted blocks. On the 

 sea bottom are also found volcanic ridges ; these are an extension of 

 volcanic ranges on land. 



(2) Bottom Deposits of the Neighbouring Seas of Japan 

 I. Bottom Deposits in General 



A. Deep Sea Bottom Deposits 



It is interesting to know that an analysis of the deep sea mud collected 

 b}^ the Hydrographic Section proved the presence of radium and calcium. 



B. Bottom Deposits of the Coasts 



Pacific Coast. — A survey of the bottom deposits in the vicinity of 

 the Izu Peninsula shows that the rocks building the adjoining land have 

 direct influence on the bottom deposits. Also a survey of the Wakasa 

 Bay shows similar results, and, furthermore, the relation between the 

 distribution of grain size and oceanic currents has been clarified. It 

 may be said that the bottom deposits of coasts is closely related to 

 crustal movement in the vicinity. xA.long the coast of Kamtchatka 

 there is exposed a fossil-bearing bed rock at the depth of about 300 

 metres, and similar phenomenon also exist in the neighbouring seas of 

 Japan down to considerable depths. Off the Kurile Islands are found 

 rather extensive Diatom deposits. 



The relation between foraminiferal communites and bottom deposits 

 has been studied in the Java Sea, and the relation between bottom 

 animals and bottom deposits in enclosed bays has been studied in various 

 parts of Japan. 



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