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
If we then descend the river from Vatteville to a place called Senneville,
we meet with a singular needle about 50 feet high, perfectly isolated on
the escarpment of chalk on the right bank of the Seine (see fig. 248.).
Another conspicuous range of inland cliffs is situated about 12 miles below
on the left bank of the Seine, beginning at Elboeuf, and comprehending the
Roches d'Orival (see fig. 249.). Like those before described, it has an
irregular surface, often overhanging, and with beds of flint projecting
several feet. Like them, also, it exhibits a white powdery surface, and
consists entirely of horizontal chalk with flints. It is 40 miles inland,
its height, in some parts, exceeding 200 feet, and its base only a few feet
above the level of the Seine. It is broken, in one place, by a pyramidal
mass or needle, 200 feet high, called the Roche de Pignon, which stands out
about 25 feet in front of the upper portion of the main cliffs, with which
it is united by a narrow ridge about 40 feet lower than its summit (see
fig. 250.). Like the detached rocks before mentioned at Senneville,
Vatteville, and Andelys, it may be compared to those needles of chalk which
occur on the coast of Normandy, as well as in the Isle of Wight and in
Purbeck[241-A] (see fig. 251.).
[Illustration: Fig. 250. View of the Roche de Pignon, seen from the south.]
[Illustration: Fig. 251. Needle and Arch of Etretat, in the chalk cliffs of
Normandy. Height of Arch 100 feet. (Passy.)[241-B]]
The foregoing description and drawings will show, that the evidence of
certain escarpments of the chalk having been originally sea-cliffs, is far
more full and satisfactory in France than in England. If it be asked why,
in the interior of our own country, we meet with no ranges of precipices
equally vertical and overhanging, and no isolated pillars or needles, we
may reply that the greater hardness of the chalk in Normandy may, no doubt,
be the chief cause of this difference. But the frequent absence of all
signs of littoral denudation in the valley of the Seine itself is a
negative fact of a far more striking and perplexing character. The cliffs,
after being almost continuous for miles, are then wholly wanting for much
greater distances, being replaced by a green sloping down, although the
beds remain of the same composition, and are equally horizontal; and
although we may feel assured that the manner of the upheaval of the land,
whether intermittent or not, must have been the same at those intermediate
points where no cliffs exist, as at others where they are so fully
developed. But, in order to explain such apparent anomalies, the reader
must refer again to the theory of denudation, as expounded in the 6th
chapter; where it was shown, first, that the undermining force of the waves
and marine currents varies greatly at different parts of every coast;
secondly, that precipitous rocks have often decomposed and crumbled down;
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