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
England; but at many points they are broken by one, two, or more ranges of
vertical and even overhanging cliffs of bare white chalk with flints. At
some points detached needles and pinnacles stand in the line of the cliffs,
or in front of them, as at _c_, fig. 245. On the right bank of the Seine,
at Andelys, one range, about 2 miles long, is seen varying from 50 to 100
feet in perpendicular height, and having its continuity broken by a number
of dry valleys or coombs, in one of which occurs a detached rock or needle,
called the Tete d'Homme (see figs. 246, 247.). The top of this rock
presents a precipitous face towards every point of the compass; its
vertical height being more than 20 feet on the side of the downs, and 40
towards the Seine, the average diameter of the pillar being 36 feet. Its
composition is the same as that of the larger cliffs in its neighbourhood,
namely, white chalk, having occasionally a crystalline texture like marble,
with layers of flint in nodules and tabular masses. The flinty beds often
project in relief 4 or 5 feet beyond the white chalk, which is generally in
a state of slow decomposition, either exfoliating or being covered with
white powder, like the chalk cliffs on the English coast; and, as in them,
this superficial powder contains in some places common salt.
[Illustration: Fig. 245. Section across Valley of Seine.]
[Illustration: Fig. 246. View of the Tete d'Homme, Andelys,
seen from above.]
Other cliffs are situated on the right bank of the Seine, opposite
Tournedos, between Andelys and Pont de l'Arche, where the precipices are
from 50 to 80 feet high: several of their summits terminate in pinnacles;
and one of them, in particular, is so completely detached as to present a
perpendicular face 50 feet high towards the sloping down. On these cliffs
several ledges are seen, which mark so many levels at which the waves of
the sea may be supposed to have encroached for a long period. At a still
greater height, immediately above the top of this range, are three much
smaller cliffs, each about 4 feet high, with as many intervening terraces,
which are continued so as to sweep in a semicircular form round an
adjoining coomb, like those in Sicily before described (p. 76.).
[Illustration: Fig. 247. Side view of the Tete d'Homme.
White chalk with flints.]
[Illustration: Fig. 248. Chalk pinnacle at Senneville.]
[Illustration: Fig. 249. Roches d'Orival, Elboeuf.]
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