CHAPTER IV 
PETROLEUM 
By W. B. Heroy 
JAPAN 
BECAUSE of the rapid growth of industrialization in 
Japan and the increasing fuel requirements of that country, 
the search for oil in the empire has been as intensive as in 
any other part of the world, and a number of petroleum 
fields have been developed. These are situated principally 
along the coast of the Sea of Japan, where there are now 
over 20 separate producing areas. 
Oil has thus far been found only in geologic formations 
of Tertiary age, chiefly Miocene and Pliocene. The areas 
of Tertiary sedimentary rocks are chiefly confined to a belt 
bordering the western margin of the archipelago, where 
the oil occurs in the main in anticlinal structures with a 
trend parallel to the general coast line. Outside of this 
Tertiary belt, in the central and eastern parts of the islands, 
the geological conditions are distinctly less favorable for 
oil accumulation. That large areas of volcanic rocks exist 
is common knowledge ; and most of the areas of sedimentary 
rocks older than the Tertiary have been closely folded and 
are more or less metamorphosed. The presence of oil 
deposits in rocks of this character is improbable and these 
regions cannot be regarded as containing commercial oil 
reserves. 
Outside of the Japanese archipelago proper a little oil 
has been found in Taiwan (Formosa). The output has 
been very disappointing and the discovery of any large fields 
in this island is improbable. A large gas field has been 
developed in the last few years, the gas being utilized for 
electric power development and in oil refining. 
Japanese Sakhalin (Karafuto) contains some areas of 
Tertiary rocks, but these are closely folded. The older rocks 
are for the most part metamorphosed. The oil possibilities