In the case of the Alps, to which we wish now specially to refer,
the chief upheaval appears to have been in Oligocene times,
although movement continued to the close of the Pliocene. There
was thus a period of some millions of years within which the
entire phenomena were comprised. Availing ourselves of Sollas'
computations,[1] we may sum the maximum depths of sedimentary
deposits of the geological periods concerned as follows:--

Pliocene - - - - - 3,950 m.

Miocene - - - - - 4,250 m.

Oligocene - - - - 3,660 m.

Eocene - - - - - - 6,100 m.

and assuming that the orogenic forces began their work in the
last quarter of the Eocene period, we have a total of 13,400 m.
as some measure of the time which elapsed. At the rate of io
centimetres in a century these deposits could not have collected
in less than 13.4 millions of years. It would appear that not
less than some ten millions of years were consumed in the genesis
of the Alps before constructive movements finally ceased.

The progress of the earth-movements was attended by the usual
volcanic phenomena. The Oligocene and Miocene volcanoes extended
in a band marked by the Auvergne, the Eiffel, the Bohemian, and
the eastern Carpathian eruptions; and, later, towards the close
of the movements in Pliocene times, the south border

[1] Sollas, Anniversary Address, Geol. Soc., London, 1909.

147

regions of the Alps became the scene of eruptions such as those
of Etna, Santorin, Somma (Vesuvius), etc.

We have referred to these well-known episodes with two objects in
view: to recall to mind the time-interval involved, and the
evidence of intense crustal disturbance, both dynamic and
thermal. According to views explained in a previous essay, the
energetic effects of radium in the sediments and upper crust were
a principal factor in localising and bringing about these
results. We propose now to inquire if, also, in the more intimate
structure of the Alps, the radioactive energy may not have borne
a part.

What we see today in the Alps is but a residue spared by
denudation. It is certain that vast thicknesses of material have
disappeared. Even while constructive effects were still in
progress, denudative forces were not idle. Of this fact the
shingle accumulations of the Molasse, where, on the northern
borders of the Alps, they stand piled into mountains, bear
eloquent testimony. In the sub-Apennine series of Italy, the
great beds of clays, marls, and limeston