But it does more. It acts as a true steam-gun, hurling into the air
fragments of cold rock rasped off from the sides of the bore, and
fragments also of melted lava, and clouds of dust, which fall again
into the sea, and form there beds either of fine mud or of breccia--
that is, fragments of stone embedded in paste. This, the reader will
understand, is no fancy sketch, as far as I am concerned. I have
steamed into craters sawn through by the sea, and showing sections of
beds of ash dipping outwards and under the sea, and in them boulders
and pebbles of every size, which had been hurled out of the crater;
and in them also veins of hardened lava, which had burrowed out
through the soft ashes of the cone. Of those lava veins I will speak
presently. What I want the reader to think of now is the immense
quantity of ash which the steam-mitrailleuse hurls to so vast a
height into the air, that it is often drifted many miles down to
leeward. To give two instances: The jet of steam from Vesuvius, in
the eruption of 1822, rose more than four miles into the air; the jet
from the Souffriere of St. Vincent in the West Indies, in 1812,
probably rose higher; certainly it met the N.E. trade-wind, for it
poured down a layer of ashes, several inches thick, not only on St.
Pages:
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160