The second European deluge is supposed to have been the result of the
formation and upheaval of the Alps. It has filled with débris and
transported material the valleys of France, Germany, and Italy over a
circumference which has the Alps for its centre. The proofs of a great
convulsion at a comparatively recent geological date are numerous. The
Alps may be from eighty to 100 miles across, and the probabilities are
that their existence is due, as Sir Charles Lyell supposes, to a
succession of unequal movements of upheaval and subsidence; that the
Alpine region had been exposed for countless ages to the action of rain
and rivers, and that the larger valleys were of pre-glacial times, is
highly probable. In the eastern part of the chain some of the Primary
fossiliferous rocks, as well as Oolitic and Cretaceous rocks, and even
Tertiary deposits, are observable; but in the central Alps these
disappear, and more recent rocks, in some places even Eocene strata,
graduate into metamorphic rocks, in which Oolitic, Cretaceous, and
Eocene strata have been altered into granular marble, gneiss, and other
metamorphic schists; showing that eruptions continued after the deposit
of the Middle Eocene formations. Again, in the Swiss and Savoy Alps,
Oolitic and Cretaceous formations have been elevated to the height of
12,000 feet, and Eocene strata 10,000 feet above the level of the sea;
while in the Rothal, in the Bernese Alps, occurs a mass of gneiss 1,000
feet thick between two strata containing Oolitic fossils.
Besides these proofs of recent upheaval, we can trace effects of two
different kinds, resulting from the powerful action of masses of water
violently displaced by this gigantic upheaval. At first broad tracks
have been hollowed out by the diluvial waves, which have, at these
points, formed deep valleys. Afterwards these valleys have been filled
up by materials derived from the mountain and transported into the
valley, these materials consisting of rounded pebbles, argillaceous and
sandy mud, generally calcareous and ferriferous. This double effect is
exhibited, with more or less distinctness, in all the great valleys of
the centre and south of France. The valley of the Garonne is, in respect
to these phenomena, classic ground, as it were.
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