24 



ART. 3. — B. KOTJ 



This gunboat-shaped islet'' (Fig. 4) presents the characteristic 

 feature of the plateau land of Kagoshima, or a marine butte, and 

 it is really a fragmentary block of the latter. Geologically, it is 

 an exact copy of the Kagoshima environs (p. 14), the lower two- 

 thirds being built up of the ash-stone or biotite- bearing hypersthene- 



Fig. 4.— Oki-Kojima vie wed southwestward from Sakura-jima. 

 O. — Oki-Kojima, cm. — Cape Sloye-zaki. 



trachyandesite"^ (PI. XVI. Fig. 1) C in Fig. 3, overlaid discordantly 

 by a thin horizontal, water-bearing bed of yellow sandy tuffite 

 which corresponds to the fossil horizon B, and lastly, the lapilli 

 bed A which makes up the upper one -third of the vertical section. 

 One can readily recognize these beds even from a distance through 

 differential erosion (Fig. 4). The andésite shows flo wage-bandings 

 which dip at high angles in different directions. The normal 

 trachyandesite is grey and light ; the grey perlitic ß type with 

 hornblende (PL XVI. Fig. 3), and the black porphyritic obsidian 

 type y (PL XVI. Fig. 2) with pyroxenes (p. 13) also occur with 

 pillow structure, indicating collectively that the ancient lavas are 

 of submarine flows. At the north end of the islet a dark-gray 



1) In 1864, it was fortified for defense against an English squadron Avhich made an 

 unsuccessful attempt of bombarding the city of Kagoshima. 



2) Some contain a large quantity of corroded quartz, and in this ease the rock may be 

 appropriately called dacite or plagioliparite. 



