F. A. Ferret — Volcanic Vortex Rings. 



411 



been formed in a bath of the magmatic gases, ont of contact 

 with the atmosphere, and at a temperature which is maintained 

 for a considerable time. The difference between the two is, 

 however, mainly physical, and the magmatic ash, if I may so 

 call it, should also, by the very conditions of its formation, be 

 virtually identical, as material, with the co-eval lava, i. e., 

 its ingredients should be the same, it should carry the same 

 salts, exhibit the same crystals under the microscope, give off 

 the same gases on being heated, etc., which could hardly be the 

 case if it were formed by the trituration of old and profoundly 



Fig. 6. 



metamorphosed rock. The limits of the present paper will not 

 permit of a full discussion of this important subject, but it may 

 be noted that Palmieri,* writing of the Vesuvian ash of 1871 

 and 1872, refers to its identity of composition with the co-eval 

 lavas, and Casoria's analyses of the 1906 products show this to a 

 remarkable degree; it is evident that some of the old tritu- 

 rated material must be found in the ash, the present contention 

 being that it does not constitute the bulk of it. 



Considering this in connection with the fact that those who 

 have attempted to calculate the total volume of material lost 

 by the cone have generally considered it insufficient to account 

 for the amount of ash emitted, we may fairly state the neces- 

 sity of admitting the emission of co-eval magmatic material 

 during the ash phase of the eruption. 



* " The Eruption of Vesuvius in 1872." L. Palmieri (page 119.) 



