of expansibility, or which happen not to have their temperature
raised at the same time, may play an important part. But as we know that
rocks have so often sunk down thousands of feet below their original
level, we can hardly doubt that much of the bending of pliant strata,
and the packing of the same into smaller spaces, has frequently been
occasioned by subsidence. Whether the failure of support be produced by
the melting of porous rocks, which, when fluid, and subjected to great
pressure, may occupy less room than before, or which, by passing from a
pasty to a crystalline condition, may, as in the case of granite,
according to the experiments of Deville, suffer a contraction of 10 per
cent., or whether the sinking be due to the subtraction of lava driven
elsewhere to some volcanic orifice, and there forced outwards, or
whether it be brought on by the shrinking of solid and stony masses
during refrigeration, or by the condensation of gases, or any other
imaginable cause, we have no reason to incline to the idea that the
consequent geological changes are brought about so suddenly, as that
large parts of continents are swallowed up at once in unfathomable
subterranean abysses. If cavities be formed, they will be enlarged
gradually, and as gradually filled. We read, indeed, accounts of
engulphed cities and areas of limited extent which have sunk down many
yards at once; but we have as yet no authentic records of the sudden
disappearance of mountains, or the submergence or emergence of great
islands. On the other hand, the creeps in coal mines[254] demonstrate
that gravitation begins to act as soon as a moderate quantity of matter
is removed even at a great depth. The roof sinks in, or the floor of the
mine rises, and the bent strata often assume as regularly a curved and
crumpled arrangement as that observed on a grander scale in
mountain-chains. The absence, indeed, of chaotic disorder, and the
regularity of the plications in geological formations of high antiquity,
although not unfrequently adduced to prove the unity and
instantaneousness of the disturbing force, might with far greater
propriety be brought forward as an argument in favor of the successive
application of some irresistible but moderated force, such as that which
can elevate or depress a continent.

In conclusion, I may observe that one of the soundest objections to the
theory of the sudden upthrow or downthrow of mountain-chains is this,
that it provid