500 ROBERT ANDERSON 



crater; and at the foot of the range on either side a fairly level plain 

 stretches off to a steep mountain wall that surrounds the bowl. At 

 only one point a break occurs in this wall. The central range is so 

 high and broad, and so completely shuts off the inclosed plain on the 

 south from the one on the north, that one does not at once recognize 

 the two plains as parts of a single great oval floor. But each of the 

 basins is so perfectly the complement of the other that little doubt 

 can exist of their being the two halves of a large crateral depression 

 partitioned off by mountains of subsequent growth. The bowl has a 

 typical caldera form, and it has most probably originated through 

 the subsidence of a formerly overlying mountain mass. It is one of 

 the very largest, if not the largest, of the craters known on this planet, 

 and without doubt the largest having such perfect preservation. 



SOURCES OF INFORMATION 



The observations upon which this article are based were made in 

 the spring of 1905, when I made a visit to the volcano and lived for 

 nearly two weeks within the caldera.^ 



Little has been known or published concerning Aso-san. John 

 Milne many years ago made a hasty visii to it and published a nar- 

 rative and descriptive article in the Popular Science Review.^ He 

 has also discussed the history of the eruptions of the new crater 

 and noted other features of the volcano in the Transactions of the 

 Seismological Society of Japan.^ Aso-san is briefly described by 

 Edmund Naumann in his paper " Ueber den Bau und die Entstehung 

 der japanischen Inseln,"^ and there is an article in Japanese on the 

 subject in the Tokio Journal of Geography, written by T. Iki.^ 



No detailed maps are available upon which to base statements 

 regarding Aso. The altitudes and other measurements here given 

 are approximate but are based on careful estimates, on barometric 

 measurements, and on general maps of Kiushiu. The accompany- 



1 In company with my brother, Malcolm Anderson, and friend, Kiyoshi Kanai, 

 to both of whom I am indebted for photographs and information. 



2 New Series, Vol. IV, No. 16, October, 1880. 



3 Vol. IX, Pt. II, 1886. 



4BerUn, R. Friedlander & Sohn, 1885. 



s Published by the Tokio Geog. Soc; Vol. XIII, No. 149, April, 1901. 



