288 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1912. 



molecular gaseous expansion and not by the crushing, of old rocks 

 nor by the collapse of crater walls. This forms a strildng example of 

 the process of ash malting as described in a paper by the present 

 writer entitled "Volcanic vortex rings and the direct formation of 

 'ash from Hquid lava" and which appears in the November issue of 

 the American Journal of Science. During tliis eruption the explo- 

 sions, although very powerful, were not sufficiently sharp to produce 

 the phenomenon of the " flasliing arcs " as observed by me at Vesuvius 

 (1906) and Etna (1910) and described in the American Journal of 

 Science. 



In addition .to the soHd blocks and the ash, a very large quantity of 

 porous, vitreous scoriae or ''lapilh" were ejected. These were of the 

 same material as the ash and containing in some cases inclusions of 

 already formed crystals of angite. In falling, they were still plastic 

 to the extent of conforming to the forked l^ranches of the Genesta 

 plants and even to be impaled upon the spines (pi. 6). 



This eruption was very instructive. A careful study was made of 

 the great "mushroom vortices" (pi. 7, fig. 1), by whose mechanism 

 heavy rocks are carried to a great height and then thrown to a dis- 

 tance by the vortex whirl. 



Some idea of the crater, 300 meters in diameter, of tliis eruption 

 may be had from plate 7, figure 2. 



On several occasions, including the present one, the writer has been 

 completely enveloped for 15 or more minutes at a time in the cloud 

 of gas and ash proceeding directly from the crater of a volcano during 

 a paroxysmal eruption. In every case there was no noxious gas — no 

 HCl, SO2, H2S, CO2 — in preceptible amounts, although these are 

 present in chstressing quantities during phases of minor activity. 

 The conclusion is inevitable that the paroxysmal gases — i. e., the gases 

 which produce a great eruption and wliich have been the cause of the 

 formation of volcanoes — consist mainly of the same ingrecUents as 

 atmospheric air. Under the above mentioned circumstances I have 

 found only a sKght feeUng of oppression, wliich may be due to the 

 high temperature or possibly to a shght deficiency in the proportion 

 of oxygen due to oxydations during the subterranean travel of the 

 gases. 



These two eruptions prove that StromboH shares in the general 

 increase of activity of the Itafiau volcanoes. 



Mount Etna is preparing for a great eruption. 



DATA OF THE ERITPTIONS 1907 AND 1912. 



1. The ash of 1907 was acid, that of 1912 alkaline, both noxious to 

 green vegetation. 



2. The paroxysmal crises of both eruptions corresjjonded with the 

 luni-solar phases, to wliich Stromboli is ver}' sensitive. 



