'602 8. Yoshiwara — On the Bonin Islands. 



group and the islands of the Sulphur Is. group, all of which are 

 also of neo-volcanic origin, are arranged in a different direction at 

 about 141° E. (Fig. 1). The second series will be a continuation of 

 the Fuji chain, as proved by the following evidence. Firstly, the 

 Ogasawara chain was constructed in the Eocene epoch; the other 

 chain belongs to a very late formation. Secondly, the second chain 

 lies exactly upon a line drawn from Mt. Fuji over Hachijo-jima as 

 far as Lot's Wife Rock. Thirdly, the volcanic activity of the Fuji 

 chain is of a later date and is not, yet extinguished, as shown in the 

 active volcano of Oshima ; eruptions frequently take place on the 

 islands south of Hachijo-jima as well as on those to the north. 

 From record we find eruptions took place on Hachijo-jima in 1487, 

 1518, 1522, 1605, and 1651, and on Aoga-shima in 1652, 1670, 

 1780, 1781, 1783, and 1785. Violent submarine eruptions occurred 

 till 1889 on the north-west of Kitaiwo-jima, by which the water 

 was raised several hundred feet above the sea-level. Even at the 

 present day we find there muddy sea-water constantly disturbed. 

 The solfataras in Iwo-jima are still constantly active. On the 

 contrary, no volcanic activities are at present observed on the 

 Ogasawara chain. The regions traversed by the Fuji chain are 

 famous for hot springs, which are also seen in the islands on the 

 southern part of the chain, namely, in Hachij5-jima at Kashidate- 

 mura, and on Mihara-yama. In Aoga-shima and Iwo-jima hot 

 springs are said to be everywhere found by digging into the ground. 

 No island of the Ogasawara group has springs either hot or cold. 

 Earthquakes are frequent on the Fuji chain, but not so in the 

 Ogasawara islands. The Fuji chain shows many local disturbances. 

 For instance, Iwo-jima is now being raised up so very quickly, that 

 ground measuring a few hundred yards was upheaved above the 

 sea-level in a few years. Very young-looking reef-corals are now 

 seen on the plateau about 300 feet above sea-level. The islands in 

 the Ogasawara chain have no sign of new upheaval ; no coral reefs, 

 excluding those of Miocene age, being there raised above the sea-level 

 even at low tide. 



Thus I come to the following conclusions : — 



Eunning parallel to the Fuji chain in the southern sea is another chain, 

 which I propose to name the " Ogasawara chain." 



The latter was formed by submarine volcanoes begun in the Eocene 

 epoch and already in repose before the Miocene, while the other chain is 

 of much later date. 



The Ogasawara chain shows andesite and variously inclined agglomerate 

 tuff, both covered with a thick horizontal Miocene limestone layer of coral 

 origin. Thus the several disturbances of the volcanic rocks and tuflfs 

 Xjreceded the formation of reefs now found as elevated reefs along the 

 ancient sea-coast. 



The Fuji chain was formed either simultaneously with or very near 

 the latter part of the formation of the Japanese Islands. The existence 

 of the still older Ogasawara chain shows that there existed already an old 

 weak line of the crust, parallel to and close by the Fuji chain, before the 

 formation of the Japanese Islands. 



