A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological MonumentsLyell, Charles, Sir
Science
A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments
Lyell, Charles, Sir
Geology
The description above given of the slanting position of the minor layers
constituting a single stratum is in certain cases applicable on a much
grander scale to masses several hundred feet thick, and many miles in
extent. A fine example may be seen at the base of the Maritime Alps near
Nice. The mountains here terminate abruptly in the sea, so that a depth of
many hundred fathoms is often found within a stone's throw of the beach,
and sometimes a depth of 3000 feet within half a mile. But at certain
points, strata of sand, marl, or conglomerate, intervene between the shore
and the mountains, as in the annexed fig. 7., where a vast succession of
slanting beds of gravel and sand may be traced from the sea to Monte Calvo,
a distance of no less than 9 miles in a straight line. The dip of these
beds is remarkably uniform, being always southward or towards the
Mediterranean, at an angle of about 25 deg.. They are exposed to view in nearly
vertical precipices, varying from 200 to 600 feet in height, which bound
the valley through which the river Magnan flows. Although in a general
view, the strata appear to be parallel and uniform, they are nevertheless
found, when examined closely, to be wedge-shaped, and to thin out when
followed for a few hundred feet or yards, so that we may suppose them to
have been thrown down originally upon the side of a steep bank, where a
river or alpine torrent discharged itself into a deep and tranquil sea, and
formed a delta, which advanced gradually from the base of Monte Calvo to a
distance of 9 miles from the original shore. If subsequently this part of
the Alps and bed of the sea were raised 700 feet, the coast would acquire
its present configuration, the delta would emerge, and a deep channel might
then be cut through it by a river.
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