F. A. Ferret — Volcanic Vortex Rings. 



409 



level in the central conduit. At the initiation of the eruption 

 the cone is fissured laterally by pressure, fusion and gas tension 

 causing- a rapid and copious outflow of lava. This is accom- 

 panied by a more or less complete demolition of the upper 

 portion of the cone, the explosive effects at the central vent 

 increase in violence, ejecting old and new material, and attain 

 their maximum with the cessation of the lava outflow, to which 

 there succeeds the truly stupendous emission of gas and ash 

 from the main crater (tig. 7) — no more liquid lava being seen. 



Fig. .4. 



But if, in such a case, we are asked to consider the liquid 

 outflow and the explosive ejections as constituting the only 

 emission of co-eval lava, and the ash as being merely old cone- 

 material and triturated rock, as is quite generally supposed, 

 then, I believe, I may raise a point of objection and interro- 



gation. 



Let us consider for a moment the condition of the magma in 

 the deeper portions of the volcanic conduit. Its temperature 

 will be higher and its gas tension greater than in the upper 

 portion while it will be subjected to "the pressure of the column 

 above it. In these respects it is analogous, as I pointed out 



