Volinno Ôsliim.i, Tdzn. 2o 



tlic oldest crater in Oshima, but a close examination does not re- 

 veal any evidence for sucli a supposition. No topographic feature 

 suggests tliat there was once a volcano having the present harbour 

 as'its cmter. There are no such magmatic materials as one would 

 expect to have issued from this crater. The lavas and éjecta ex- 

 posed on the encircling wall are nothing lut those of the somma 

 as is clear from then- dipping directions (generally toward the 

 ' southeast), as well as from their pétrographie characteristics. 



It would seem more probable that this Habu crater was 

 formed by a sudden blowing away of the suvliciul layers of lavas 

 and éjecta on the flat land at the soutlieastern foot of the somma 

 (pp. 17-18). 



The probability of this inference is further strengthened by 

 the exposures on the crater wall. In Fig. 13 the lava marked 

 Q shows a slaggy surface on the left hand side of P, while on 

 its opposite side a compact mner part is exposed. The exposure 

 of the compact inner part is attributable to the removal of the 

 slaggy surficial part by explosive action thus leaving tlie latter on 

 the left side of point P. 



This explosion was - phreatlc-'' following Suess's term, being 

 absolutely unaecon.panied by any extrusion of incandescent ma- 

 terials, either fluent or pyroclastic. Angular blocks of lava are 

 fonnd scattered in the vicinity of Habu, and if these represent the 

 explosion products of the crater in question, as seems to be high- 

 ly probable, it follows that the Habu explosion mnst have taken 

 place at a very late stage of the volcanic history as these blocks 

 of lava are almost free from the covering of any later materials. 

 According to historic records, Habu harbour was once a 



1) Cited by Dalï in his Igryeous Mocks and Thtlr Orlfm, 1914. 



