ally converted into
_tangential pressures_, the contraction of the nucleus now beginning to
exceed (for equal losses of heat) that of the crust through which it
cooled. At this stage these tangential pressures gave rise to the
_chief_ elevations of mountain chains--not by liquid matter by any
process being injected from beneath vertically, but by such pressures,
mutually reacting along certain lines, being resolved into the vertical,
and forcing upwards more or less of the crust itself. The great outlines
of the mountain ranges and the greater elevation of the land were
designated and formed during the long periods that elapsed in which the
continually increasing thickness of crust remained such that it was
still, as a whole, flexible enough, or opposed sufficiently little
resistance to crushing, to admit of this uprise of mountain chains by
resolved tangential pressures. I have shown that the simple mechanism of
such tangential pressures is competent to account for all the complex
phenomena both of the elevations and of the _depressions_ that we now
see on the earth's surface (other than continents and ocean beds),
including the production of gaping fissures (in directions generally
orthogonal to those of tangential pressure). And as our earth is still a
cooling body, and the crust, however now thicker and more rigid, is
still incapable of sustaining the tangential pressures to which it is
now exposed, so I by no means infer that slow and small (relatively)
movements of elevation and depression may not be still and now going on
upon the earth's surface; in fact all the phenomena of elevation and
depression, rending, etc., which at a much remoter epoch acted upon a
much grander and more effective scale. So that, for aught my views say
to the contrary, all the mountain chains in the world may be possibly
increasing in stature year by year, or at times; but in any case at a
rate almost infinitesimally small in its totality over the whole earth
to that with which their ridges were originally upreared.

But the thickness of the earth's crust--thus constantly added to, by
accretion of solidifying matter from the still liquid or pasty nucleus,
as the whole mass has cooled--has now assumed such a thickness as to be
able to offer a too considerable resistance to the tangential pressures,
to admit of its giving way to any large extent by resolution upwards;
yet the cooling of the whole mass is going on, and contraction, though
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