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1. 
‘Parr I Sucr.i.§2] VOLCANIC EXPLOSIONS.  —_—_-215 
line of a fissure, either from the congelation of the lava round the 
point of emission, or from the accumulation of ejected scoriz round 
the fissure-vent. 
_Explosions.—Apart from the appearance of visible fissures, 
volcanic energy may be, as it were, concentrated on a given point, 
which will usually be the weakest in the structure of that part of the 
terrestrial crust, and from which the solid rock, shattered into pieces, is 
hurled into the air, followed by the ascent of volcanic materials. 
This operation has often been observed in volcanoes already formed, 
and has even been witnessed on ground previously unoccupied by a 
voleanic vent. The history of the cone of Vesuvius brings before us 
a long series of such explosions, beginning with that of 79—and 
coming down to the present day. Even now, in spite of all the lava 
and ashes poured out during the last eighteen centuries, it 1s easy to 
see how stupendous must have been that earliest explosion, by which 
thesouthern half of the ancient crater was blown out. At every 
successive important eruption, a similar but minor operation takes 
place within the present cone. The hardened cake of lava forming 































































































































































































































































































































































Fic. 38.— View oF VESUVIUS FROM THE SOUTH, 
Showing the remaining part of the old crater-wall of Somma behind. 
the floor is burst open, and with it there usually disappears much of 
the upper part of the cone, and sometimes, asin 1872, a large segment 
of the crater-wall. The islands of Santorin (Figs. 58 and 59) bring 
before us evidence of a prehistoric catastrophe of a similar nature, by 
which a large volcanic cone was blown up. The existing outer islands 
are a chain of fragmenis of the periphery of the cone, the centre of 
which is now occupied by the sea. In the year 1538 a new volcano, 
Monte Nuovo, was formed in 24 hours on the margin of the Bay of 
Naples. An opening was drilled by successive explosions, and such 
quantities of stones, scoriz, and ashes were thrown out from it as to 
form a hill that rose 440 English feet above the sea-level, and was 
more than a mile and a half in circumference. Most of the fragments 
now to be seen on the slopes of this cone and inside ils beautifully 
