wherever river discharge is distributing the sediments over the sea-floor, or the lime-secreting organisms are actively at work.  And yet it took but a few millions of years to uplift the deposits of the ancient Tethys; pile high its sediments in fold upon fold in the Alps, the Carpathians, and the Himalayas; and—­exposing them to the rigours of denudation at altitudes where glaciation, landslip, and torrent prevail—­inaugurate a new epoch of sedimentation and upheaval.

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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.

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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,