[1] Schmidt, Ec.  Geol. Helvelix, vol. ix., No. 4, p. 590

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If time be given for the heat to accumulate in the lower depths of the crushed-up sediments, here is an additional source of increased temperature.  The piled-up masses of the Simplon might have occasioned a rise due to radioactive heating of one or two hundred degrees, or even more; and if this be added to the interior heat, a total of from 800 deg. to 1000 deg. might have prevailed in the rocks now exposed at the surface of the mountain.  Even a lesser temperature, accompanied by the intense pressure conditions, might well occasion the appearances of thermal metamorphism described by Weinschenk, and for which, otherwise, there is difficulty in accounting.[1]

This increase upon the primarily developed temperature conditions takes place concurrently with the progress of compression; and while it cannot be taken into account in estimating the conditions of initial yielding of the crust, it adds an element of instability, 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