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 series of formations in the cliffs of eastern Norfolk, now under
consideration, beginning with the lowest, is as follows:--First, chalk;
secondly, patches of a marine tertiary formation, called the Norwich
Crag, hereafter to be described; thirdly, the freshwater beds already
mentioned; and lastly, the drift. Immediately above the chalk, or crag,
when that is present, is found here and there a buried forest, or a
stratum in which the stools and roots of trees stand in their natural
position, the trunks having been broken short off and imbedded with
their branches and leaves. It is very remarkable that the strata of the
overlying boulder formation have often undergone great derangement at
points where the subjacent forest bed and chalk remain undisturbed.
There are also cases where the upper portion of the boulder deposit has
been greatly deranged, while the lower beds of the same have continued
horizontal. Thus the annexed section (fig. 114.) represents a cliff
about 50 feet high, at the bottom of which is _till_, or unstratified
clay, containing boulders, having an even horizontal surface, on which
repose conformably beds of laminated clay and sand about 5 feet thick,
which, in their turn, are succeeded by vertical, bent, and contorted
layers of sand and loam 20 feet thick, the whole being covered by flint
gravel. Now the curves of the variously coloured beds of loose sand,
loam, and pebbles are so complicated that not only may we sometimes
find portions of them which maintain their verticality to a height
of 10 or 15 feet, but they have also been folded upon themselves in
such a manner that continuous layers might be thrice pierced in
one perpendicular boring.
[Illustration: Fig. 114. Cliff 50 feet high between Bacton
Gap and Mundesley.]
[Illustration: Fig. 115. Folding of the strata between East
and West Runton.]
[Illustration: Fig. 116. Section of concentric beds west of Cromer.
1. Blue clay.
2. White sand.
3. Yellow Sand.
4. Striped loam and clay.
5. Laminated blue clay.]
At some points there is an apparent folding of the beds round a central
nucleus, as at _a_, fig. 115., where the strata seem bent round a small
mass of chalk; or, as in fig. 116., where the blue clay, No. 1., is in the
centre; and where the other strata, 2, 3, 4, 5, are coiled round it; the
entire mass being 20 feet in perpendicular height. This appearance of
concentric arrangement around a nucleus is, nevertheless, delusive, being
produced by the intersection of beds bent into a convex shape; and that
which seems the nucleus being, in fact, the innermost bed of the series,
which has become partially visible by the removal of the protuberant
portions of the outer layers.
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