Man and the Glacial PeriodWright, G. Frederick (George Frederick)
History
Man and the Glacial Period
Wright, G. Frederick (George Frederick)
Glacial epoch; Prehistoric peoples
"The way in which the boulder-clay is related to the rocks upon which
it rests is a conclusive condemnation of any theory of floating ice;
for example, where it rests upon Oxford Clay, it contains the fossils
characteristic of that formation, as it is largely made up of the clay
itself. The exceptions to this rule are as suggestive as those cases
which conform to it. Each outcrop yields material to the boulder-clay to
the south westward, showing a pull-over from the northeast.
"One of the most remarkable features of the drift of this part of
England is the inclusion of gigantic masses of rock transported for
a short distance from their native outcrop, very often with so small
a disturbance that they have been mapped as _in situ_. Examples of
chalk-masses 800 feet in length, and of considerable breadth and
thickness, have been observed in the cliffs near Cromer, in Norfolk, but
they are by no means restricted to situations near the coast. One example
is mentioned in which quarrying operations had been carried on for some
years before any suspicion was aroused that it was merely an erratic.
The huge boulders were probably dislodged from the parent rock by the
thrust of a great glacier, which first crumbled the beds, then sheared
off a prominent fold and carried it along. This explanation we owe to Mr.
Clement Reid.[BS] The drift-deposits of this region frequently contain
shells, but they rarely constitute what may be termed a consistent fauna,
usually showing such an association as could only be found where some
agent had been at work gathering together shells of different habitats
and geological age.
[Footnote BS: See Geology of the Country around Cromer, and Geology of
Holderness, Memoirs of Geological Survey of England and Wales.]
[Illustration: Fig. 45.--Section at right angles to the cliff through
the westerly chalk bluff at Trimingham, Norfolk, showing the manner in
which chalk masses are incorporated into the till (Clement Reid). Scale,
250 fret to an inch. A. Level of low-water spring-tides; B. Chalk, with
sandy bed at *; C. Forest-bed series, etc., seen in the cliffs a few
yards north and south of this point; D. Cromer till, stiff lead-colored
boulder-clay; E. Fine, chalky sands, much false-bedded; F. Contorted
drift, brown bouldery-clay with marked bedding- or fluxion-structure; G.
The bed, above the white line were seen and measured by more snow and
measured by Mr. Reid; * Chalk seen _in situ_ on beach.
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Elsewhere in the archive
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account