80 REPORT—1850. 
up and shatter the bottom, and scatter the molten matter, or may provide 
the conditions for successive shocks; but the above seems to account for the 
general facts. 
Again, if the eruption occur under land communicating with the sea by 
rents and fissures, and steam be generated therein, or be blown continuously 
for a longer or shorter time from them into the sea-water, its unequal and 
per saltum condensation under pressure, will produce all that trembling and 
repercussion, which, transmitted, will form the earthquake. The phenomena of 
fluids in the spheroidal state, first systematized by Boutigny, though observed 
in part long before, seem to remove the great difficulty that Gay-Lussac 
found in admitting the possibility, of access of sea-water to volcanic vents, 
viz. that it could not gain access against a pressure capable of sustaining co- 
lumns of fluid lava 7000 or 8000 feet deep. Let us now remember that 
water and white-hot lava might be stirred up together in a huge caldron, 
as one would shake oil and water together, and there would be no repulsion, 
no explosions, until the lava had cooled down nearly to blackness, when the 
whole mass would be suddenly and with explosion shattered into fragments 
from the steam evolved in all its cells. Compare Dolomieu, ‘ Deser. Calab. 
Earthquake.’ 
I do not regard these views as wholly conjectural. I conceive the facts 
known are sufficient to enable us to say, that they are a true, though pro- 
bably most incomplete statement of the operations in nature; and it is 
remarkable, that not only that most accurate observer, Aristotle, was struck 
with the similarity of the sound and trembling motion to the ebullition of 
steam in water, but we have seen a long-practised observer compare his 
experience of South American earthquake sounds and shocks to the blowing 
of steam through the tender of a locomotive engine; and that some have 
compared the first noise of the coming shock to that of a large piece of red- 
hot iron quenched in cold water; while Mrs. Maria Graham, in her account 
of the earthquaké at Chili, in 1822 (Geol. Trans. 2nd ser. vol. i. p. 414), 
says she felt “a general tremor and a sound like that of vapour bursting 
out, similar to the tremor and sound which she remembered to have observed 
at each jet of fire while standing on the cone of Vesuvius during the erup- 
tion of 1818.” 
Briefly, then, it seems to me, that, however modified, the immediate im- 
pulses producing earth-waves of shock are due— 
Ist. To the sudden formation of steam from water previously i in a state of 
repulsion from the heating surfaces, (spheroidal state) and which may 
or may not be again suddenly condensed under pressure of sea-water. 
2nd. To the evolution of steam through fissures, and its irregular and 
per saltum condensation under pressure of sea-water. 
3rd. To great fractures and dislocations in the rocky crust, suddenly 
produced by pressure acting on it from beneath, or in any other 
direction. 
4th. Occasionally, but rarely, to the recoil from mighty explosive effects 
at volcanic foci, as when a mass of rock weighing 200 tons was shot 
from the crater of Cotopaxi to the distance of nine miles (Humboldt), 
or when nearly one-half of the crater of Vesuvius was blown away. 
In such cases the shock from recoil must have been far greater than upon 
any occasions when powder magazines have been blown up. Yet during the 
last century, when a powder-mill at Waltham-abbey exploded, the inha- 
bitants of districts so far removed as not to know the true nature of the case, 
felt the shock, and had their furniture and houses, &c. so shaken, as to conclude 
that it was the shock of an earthquake due to natural causes. ( Annual Reg.) 
And numerous instances will be found in the pages of the ‘ Gent. Mag.’ of 
