ON THE VOLCANIC PHENOMENA OF JAPAN. 



425 



4. Position and Relative Age of Japanese Volcanoes. 



The youngest of the Japanese volcanoes appear to be those which 

 •exist as or on small islands. On the islands in the Kuriles, in the 

 Oshima Group, and in the Satsuma Sea, many of the volcanoes are yet 

 young and vigorous. Further, many of these islands have been formed 

 during the historical period. The island-forming period in the Satsuma 

 Sea occurred about the year 1780. 



Looked at generally, the volcanoes of Japan form a long chain running 

 from the N.E. towards the S.W. A closer examination of the distribu- 

 tion of the volcanic vents shows that there are probably four lines. 



1. The N.E. S.W. line running from Kamtschatka through the Kuriles 

 and Northern Tezo. 



2. The curved line following the backbone of Honshiu and terminating 

 ■on the western side of the Yezo anticlinal. 



3. The N.N.W. S.S.E. line of the Oshima Group. This line, coming 

 from the Ladrones, passes through Oshima and Fujisan pai-allel to and 

 near to the line of a supposed fault. Here it intersects the main line 

 running through Honshiu. Volcanic vents are here very numerous. As 

 the Honshiu line is intersected, while the Oshima line is the intersector, 

 it may be argued that the Oshima- Fujisan line of volcanoes are younger 



than many of those on the Honshiu line. 



4. The Satsuma line, coming from the Philippines through Sakurajima 

 and culminating in the famous Mount Aso, which is the nucleus of Kiushiu. 



6. Lithological and Chemical Character of Lavas. 



Although I have made an extensive collection of the volcanic rocks of 

 this country, opportunity has not hitherto presented itself for their 

 examination. I can therefore only speak of them in general terms. They 

 are now, I believe, being carefully studied by the officers of the geological 

 survey of Japan. The rocks in my possession are chiefly andesites. 

 Those containing augite, like the rocks of Fujisan, as pointed out by 

 Mr. Wada, the director of the geological survey, closely approximate to 

 basalts. True basalt is, however, rare. Another common rock is horn- 

 blende andesite, some of which contains free quartz. Quartz trachytes 

 occur in the north of Japan. The following table, which is chiefly drawn 

 np from material kindly placed at my disposal by Mr. "Wada, shows the 

 percentages of silica, ferrous and ferric oxide contained in the rocks of 

 ten volcanoes : 



Peecentage of Sio., FeO and Fe.. 



O3 IN THE Volcanic Books of Japan. 



Locality 



1. Norikura ..... 



2. Mitake 



3. Kusatsu (near Zi goedo Amiguchi) 



4. Amagi (Hakone) 



5. Komagadake .... 



6. Moriyoshisan . 



7. Chokai 



8. Hakone (Tonosawa) 



9. Fujisan 

 10. Oshima 



Sio.e 



FeO 



6L72 

 59.97 

 61.49 

 65.34 

 56.27 

 56.17 

 ( 60.64 

 1 54.55 

 48.97 

 49.00 

 52-00 



1.35 

 3.27 

 3.30 

 2.45 

 2.19 

 2.65 

 3.81 

 5.19 

 4.02 

 5.1 

 13.70 (?) 



Fe.o O, 



3.50 

 3.86 

 4.35 

 3.09 

 6.69 

 4.15 

 3.14 

 4.42 

 4.81 

 6.06 



