r with an immense number of cattle, partly by
the depredations of the lava, partly by the noxious vapors which
impregnated the air, and, in part, by the famine caused by showers of
ashes throughout the island, and the desertion of the coasts by the
fish.

_Immense volume of the lava._--But the extraordinary volume of melted
matter produced in this eruption deserves the particular attention of
the geologist. Of the two branches, which flowed in nearly opposite
directions, the greatest was fifty, and the lesser forty miles in
length. The extreme breadth which the Skapta branch attained in the low
countries was from twelve to fifteen miles, that of the other about
seven. The ordinary height of both currents was one hundred feet, but in
narrow defiles it sometimes amounted to six hundred. Professor Bischoff
has calculated that the mass of lava brought up from the subterranean
regions by this single eruption "surpassed in magnitude the bulk of Mont
Blanc."[586] But a more distinct idea will be formed of the dimensions
of the two streams, if we consider how striking a feature they would now
form in the geology of England, had they been poured out on the bottom
of the sea after the deposition and before the elevation of our
secondary and tertiary rocks. The same causes which have excavated
valleys through parts of our marine strata, once continuous, might have
acted with equal force on the igneous rocks, leaving, at the same time,
a sufficient portion undestroyed to enable us to discover their former
extent. Let us, then, imagine the termination of the Skapta branch of
lava to rest on the escarpment of the inferior and middle oolite, where
it commands the vale of Gloucester. The great platform might be one
hundred feet thick, and from ten to fifteen miles broad, exceeding any
which can be found in Central France. We may also suppose great tabular
masses to occur at intervals, capping the summit of the Cotswold Hills
between Gloucester and Oxford, by Northleach, Burford, and other towns.
The wide valley of the Oxford clay would then occasion an interruption
for many miles; but the same rocks might recur on the summit of Cumnor
and Shotover Hills, and all the other oolitic eminences of that
district. On the chalk of Berkshire, extensive plateaus, six or seven
miles wide, would again be formed; and lastly, crowning the highest
sands of Highgate and Hampstead, we might behold some remnants of the
current five or six hundred feet i