THE GREAT ERUPTION OF SAKURA-JIMA IN 1914. 19 



abundant literature on the eruption by specialists as well as 

 by laymen is diffused with phrases of the same tone. But so far 

 as the writer's knowledge goes, no one has ever studied seriously 

 the geology, the mode of formation and the age of tectonic move- 

 ment in the bay. For this reason, the writer has indulged some- 

 what in detail on the above subjects. 

 Epitome rpj-^^ geology of the rogiou, briefly told, is this : 



OF TSEj 



Geology rj,]^^ regiou arouud Kagoshiuia Bay is built up of 

 Mesozoic slate and batholithic granite. On the eroded surface of 

 submerged land deposited locally the Tertiary formation, whicli 

 was later partially upheaved and eroded. Then \Tilcanism was 

 called into play in the shallow sea, when the ash-stone C (Fig. 3) 

 poured out, catching fragments of slate, which solidified under 

 water as soaking stone and spherulitefels. Then sands and gravel 

 B, products of erosion, deposited with marine shells. Vulcanism 

 was still in full force, ejecting submarine pumice and lapilli A, 

 which were deposited to a great tliickness of 100 m. or more. 



Meanwhile the sea was sinking while deposition was going 

 on. Finally, the land was upheaved to 230 m. forming a 

 monotonous lapilli plateau which characterizes the region (PL IV. 

 Fig. 1). The long interval of vulcanism corresponds to the later 

 Tertiary or early DUuülal tlms, which we know by the evidence 

 of fossils. Cotemporaneous with that upheaval, vertical dis- 

 placement of 430 m. took place, thereby creating the trough-bay 

 of Kagoshima. The whole coastline of Kyiishii was remodeled 

 during this period. 



It is contrary to an assertion often made recently that here 

 volcanoes find their vents in the sunken bottom, as Sakura-jima 

 and Kaimon, instead of the highland margin of the tectonic 

 graben. The writer is inclined to think that volcanic vents find 



