ME. EOBERT MALLET ON VOLCANIC ENERGY. 
211 
crushed rock; but, as before, we assume the lift to be 10 miles (and not from sea-level 
to centre of gravity of the cone), or 21 times nearly the above. 
TIence we have for the total work of the “cone building” in elevation, heating, and 
fusing (taken, as in the previous case, at 3’92 cubic miles of mean crushed rock to each 
cubic mile of volcanic cone material) as follows : — 
Total lifting work and waste ’000315 
Heating and fusing work on ’000743 cubic miles of cone material . ’00291 
Total in mean crushed rock in cubic miles per annum *000606 
197. Now the total number of active volcanic foci known on our globe, as given by 
Humboldt and others, is 270 ; let us take them at 300, and that all, small and great, when 
active are as active as Vesuvius, and produce the same average annual amount of equally 
heated or fused ejecta while in a state of activity. Both assumptions are greatly above 
the truth, probably, when we consider how many very small volcanoes there are (such as 
Stromboli) always active, but whose ejecta in a year (at present and for all history) have 
been insignificant in proportion to the few very great ones and the immense periods 
of dormancy of the majority. How many of the active volcanoes are on the average 
in eruption every year we know not ; it will be admitted as probably above the truth if 
we assume that one in every three of them is so; that amounts to 100 cones always at 
work, at the rate of activity which we have taken for Vesuvius, which is notoriously 
one of the most frequently active on the globe 
The final result, then, is that — Qx 00Q606 , — -0606 cubic mile, represents in crushed 
rock per annum a considerable excess above the total existing annual vulcanicity expended 
on our earth. 
198. [Another form of estimate may be employed. The following are amongst the 
greatest single flows of lava of which any attempt has been made to approximate to their 
volume : — 
Graveneire 
. . 57 million cubic metres. 
Pariou ....... 
Mont Sinuire . 
172 million cubic metres. 
Come 
These are all in Auvergne, as given by M. Le Coq (Epoques Geolog. cl Auvergne, t. iv.), 
who states the great uncertainty attending the cubation of every lava-stream, and 
deems that of Come as very doubtful. 
Skaptar Jokul,17S3: 164 millions=1640 millions of cubic metres (Voy. en Islande,&c.). 
I omit another from the same work, affirmed, on utterly fallacious data, to have 
exceeded the volume of the entire mass of Mont Blanc. 
* The catalogues that exist of the periods of activity and of rest of Iceland, Etna, and Vesuvius appear to 
contain the fact that in those cases at least the years of activity to those of dormancy do not reach one in three 
(see Daubeny’s ‘Volcanoes’ and Phillips’s ‘Vesuvius’). 
MDCCCLXXIII. 2 F 
