GENERAL CHARACTERISTICS OF FAR EASTERN SEAS 



685 



diatomaceous oozes (Fig. 326) ; this is the result of the intensive development 

 of diatoms in these regions. 



Geological past of the Far Eastern Seas 



The problem of the geological past and the palaeogeography of the Far Eastern 

 Seas is exceptionally important. The nature of the alterations endured and the 

 differences in the past of the Seas of Japan and of Okhotsk and the Bering 



Fig. 326. Distribution of deposits of amorphous 

 silica produced by diatoms (as percentage of dry 

 weight of soil) (Bezrukov): 1 Less than 1%; 

 2 From 10 to 20% ; 3 From 20 to 30% ; 4 More than 

 30%. 



Sea during the Tertiary and Quaternary Periods are two most important 

 problems. 



In his work on the Quaternary geology of Hokkaido Island the Japan- 

 ese geologist Minato (1955) maintains the existence of a strong mainland 

 glaciation in the Ice Age, noting its traces on Hokkaido Island. Having 

 examined all the available data he considers there were two periods of con- 

 siderable fall of temperature (two Ice Ages, one much earlier than the other) 

 and great fluctuations of the sea-level, marked by a series of terraces at 

 different horizons up to a height of 200 m above sea-level. On the other side 

 Minato envisages considerable shifts of the coastline to seaward, during which 

 the Islands of Japan must have been joined to the mainland. 



The Tertiary and Quaternary Periods of the history of the Far Eastern Seas 

 are characterized by the difference in the past of the Bering and Okhotsk 

 Seas on the one hand and that of the Sea of Japan on the other. The first two 

 basins retained their broad link with the Ocean ; the past of the Sea of Japan 



