658 SueKOZU 
The most striking physical feature of Dozen is the circular 
arrangement of the three main islands. The largest island, 
Nishino-shima (55.23 sq. km.), lies on the northwest of the group; 
the smaller one, Nakano-shima (35.20 sq. km.), on the east; and 
the smallest, Chiburi-shima (14.82 sq. km.), on the south. An 
inland sea with an area of about 51.24 square kilometers is 
inclosed by the three islands. The most prominent peak, called 
Takuhi-yama (Fig. 2), 525 meters in height, is situated south of 
the middle part of Nishino-shima. The sea coast facing the ocean 
ends abruptly, as is the case at Dogo, and the slope of the islands 
is steeper toward the inner side than toward the outer. Dr. T. 
Harada compared the form of D6ézen with that of Santorin in the 
Mediterranean. 
Fic. 1.—Dé6go as seen from the south 
Geological sketch of the Oki Islands.—In order to give a general 
idea of the structure of the Oki Islands, their geological features will 
be described briefly. The geological formations of the islands, in 
the order of their age from younger to older, are as follows: 
. Alluvium. 
. Trachydolerites and basalts. 
. Diluvium (?). 
. Trachytes. 
. Trachyandesites and trachydolerites. 
. Trachytic rhyolites. 
. Greenish trachyandesites. 
. Soda-rhyolites. 
g. Schistose granites and quartz-syenites. 
to. Andesites. 
11. Tertiary strata. 
CON AM BW DN H 
The islands consist mainly of volcanic rocks, which were 
erupted at several times, probably from the middle of the Tertiary 
