142 8. SEKIYA AND Y. KIKUCHI 



Bandai, though classified as active, have never, within historic times, 

 shown a true lava eruption. And this may be said to hold good for 

 most of the active volcanoes on the Main Island. In fact, most of 

 them, which had their climax of activity during Tertiary times, are 

 now verging to extinction. This is due to the general and gradual 

 abatement of volcanic force since the end of the Tertiary Era. Any 

 great geologic changes which have taken place since then, have had 

 to do with the general rise of the land surface above the sea-level. At 

 present the Tertiary strata, some three or four hundred metres above 

 the sea-level, cover a large part of the whole area of Japan. They con- 

 sist principally of tufaceous deposits, are mostly of marine origin, and 

 are often found surrounding or even underlying the volcanoes. These 

 volcanoes would thus seem to have attained their maximum intensity 

 at a time when proximity to the sea greatly favoured their activity. 

 But the subsequent gradual rising of the land surface has had the 

 effect of shifting the volcanoes further and further from the sea-board, 

 thus greatly mitigating their action. 



The eruptions which are usually experienced in these volcanoes 

 in modern times seem to be essentially superficial. The recent cata- 

 strophe of Bandai may indeed be taken as a grand example of this 

 kind of volcanic manifestation and may well be called an explosive 

 eruption. The great horse-shoe-like chasm opened toward the north 

 may be called an explosion-crater. Its appearance from the north side 

 (fig. 1, PI. XVI, and tig. 1, PI. XXI) presents a striking resemblance 

 to the deep chasms which are often characteristic of certain volcanoes, 

 e.g., the 'Val del Bove' of Etnn, the Caldera of Palma, &c, and at 

 the same time suggests similarity of origin. 



Perhaps it may be of interest here to refer to a volcanic outburst 

 which occurred in Japan early last century and which seems to have 

 strongly resembled the present Bandai éruptions It is the great lateral 



