stability, inasmuch as any progressive thickening by lateral
compression results in an accelerated rise of the goetherms. It
is probable that time sufficient for these effects to develop, if
not to their final, yet to a considerable extent, is often
available. The viscous movements of siliceous materials, and the
out-pouring of igneous rocks which often attend mountain
elevation, would find an explanation in such temperatures.

[1] Weinschenk, _Congres Geol. Internat._, 1900, i., p. 332.

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There is no more striking feature of the part here played by
radioactivity than the fact that the rhythmic occurrence of
depression and upheaval succeeding each other after great
intervals of time, and often shifting their position but little
from the first scene of sedimentation, becomes accounted for. The
source of thermal energy, as we have already remarked, is in fact
transported with the sediments--that energy which determines the
place of yielding and upheaval, and ordains that the mountain
ranges shall stand around the continental borders. Sedimentation
from this point of view is a convection of energy.

When the consolidated sediments are by these and by succeeding
movements forced upwards into mountains, they are exposed to
denudative effects greatly exceeding those which affect the
plains. Witness the removal during late Tertiary times of the
vast thickness of rock enveloping the Alps. Such great masses are
hurried away by ice, rivers, and rain. The ocean receives them;
and with infinite patience the world awaits the slow accumulation
of the radioactive energy beginning afresh upon its work. The
time for such events appears to us immense, for millions of years
are required for the sediments to grow in thickness, and the
geotherms to move upwards; but vast as it is, it is but a moment
in the life of the parent radioactive substances, whose atoms,
hardly diminished in numbers, pursue their changes while the
mountains come and go, and the

133

rudiments of life develop into its highest consummations.

To those unacquainted with the results of geological
investigation the history of the mountains as deciphered in the
rocks seems almost incredible.

The recently published sections of the Himalaya, due to H. H.
Hayden and the many distinguished men who have contributed to the
Geological Survey of India, show these great ranges to be
essentially formed of folded sediments penetrated by vast masses
of granite and o