out whole geological periods, so as to become
partially separated from the nucleus, until at last it gives way
suddenly, cracking and falling in along determinate lines of fracture.
During such a crisis the rocks are subjected to great lateral pressure,
the unyielding ones are crushed, and the pliant strata bent, and are
forced to pack themselves more closely into a smaller space, having no
longer the same room to spread themselves out horizontally. At the same
time, a large portion of the mass is squeezed upwards, because it is in
the upward direction only that the excess in size of the envelope, as
compared to the contracted nucleus, can find relief. This excess
produces one or more of those folds or wrinkles in the earth's crust
which we call mountain-chains.

"Lastly, some chains are comparatively modern; such as the Alps, which
were partly upheaved after the middle tertiary period. The elevation of
the Andes was much more recent, and was accompanied by the simultaneous
outburst for the first time of 270 of the principal volcanoes now
active.[243]

"The agitation of the waters of the ocean caused by this convulsion
probably occasioned that transient and general deluge which is noticed
in the traditions of so many nations."[244]

Several of the topics enumerated in the above summary, such as the cause
of interruptions in the sedimentary series, will be discussed in the
thirteenth chapter, and I shall now confine myself to what I conceive to
be the insufficiency of the proofs adduced in favor of the suddenness of
the upthrow, and the contemporaneousness of the origin of the parallel
chains referred to. At the same time I may remark, that the great body
of facts collected together by M. de Beaumont will always form a most
valuable addition to our knowledge, tending as they do to confirm the
doctrine that different mountain-chains have been formed in succession,
and, as Werner first pointed out, that there are certain determinate
lines of direction or strike in the strata of various countries.

The following may serve as an analysis of the evidence on which the
theory above stated depends. "We observe," says M. de Beaumont, "when we
attentively examine nearly all mountain-chains, that the most recent
rocks extend horizontally up to the foot of such chains, as we should
expect would be the case if they were deposited in seas or lakes, of
which these mountains have partly formed the shores; whilst the other
sedimentar