which this single convulsion
occasioned, if the extent of country moved upward really amounted to
100,000 square miles,--an extent just equal to half the area of France,
or about five-sixths of the area of Great Britain and Ireland. If we
suppose the elevation to have been only three feet on an average, it
will be seen that the mass of rock added to the continent of America by
the movement, or, in other words, the mass previously below the level of
the sea, and after the shocks permanently above it, must have contained
fifty-seven cubic miles in bulk; which would be sufficient to form a
conical mountain two miles high (or about as high as Etna), with a
circumference at the base of nearly thirty-three miles. We may take the
mean specific gravity of the rock at 2.655,--a fair average, and a
convenient one in such computations, because at such a rate a cubic yard
weighs two tons. Then, assuming the great pyramid of Egypt, if solid, to
weigh, in accordance with an estimate before given, six million tons, we
may state the rock added to the continent by the Chilian earthquake to
have more than equalled 100,000 pyramids.

But it must always be borne in mind that the weight of rock here alluded
to constituted but an insignificant part of the whole amount which the
volcanic forces had to overcome. The whole thickness of rock between the
surface of Chili and the subterranean foci of volcanic action may be
many miles or leagues deep. Say that the thickness was only two miles,
even then the mass which changed place and rose three feet being 200,000
cubic miles in volume, must have exceeded in weight 363 million
pyramids.

It may be instructing to consider these results in connection with
others already obtained from a different source, and to compare the
working of two antagonistic forces--the levelling power of running
water, and the expansive energy of subterranean heat. How long, it may
be asked, would the Ganges require, according to data before explained
(p. 283), to transport to the sea a quantity of solid matter equal to
that which may have been added to the land by the Chilian earthquake?
The discharge of mud in one year by the Ganges was estimated at 20,000
million cubic feet. According to that estimate it would require about
four centuries (or 418 years) before the river could bear down from the
continent into the sea a mass equal to that gained by the Chilian
earthquake. In about half that time, perhaps, the united wate