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
To the north of Cromer are other fine illustrations of contorted drift
reposing on a floor of chalk horizontally stratified and having a level
surface. These phenomena, in themselves sufficiently difficult of
explanation, are rendered still more anomalous by the occasional inclosure
in the drift of huge fragments of chalk many yards in diameter. One
striking instance occurs west of Sherringham, where an enormous pinnacle of
chalk, between 70 and 80 feet in height, is flanked on both sides by
vertical layers of loam, clay, and gravel. (Fig. 117.)
[Illustration: Fig. 117. Included pinnacle of chalk at Old Hythe point,
west of Sherringham.
_d._ Chalk with regular layers of chalk flints.
_c._ Layer called "the pan," of loose chalk, flints, and marine shells
of recent species, cemented by oxide of iron.]
This chalky fragment is only one of many detached masses which have been
included in the drift, and forced along with it into their present
position. The level surface of the chalk _in situ_ (_d_) may be traced for
miles along the coast, where it has escaped the violent movements to which
the incumbent drift has been exposed.[129-A]
We are called upon, then, to explain how any force can have been exerted
against the upper masses, so as to produce movements in which the
subjacent strata have not participated. It may be answered that, if we
conceive the _till_ and its boulders to have been drifted to their
present place by ice, the lateral pressure may have been supplied by the
stranding of ice-islands. We learn, from the observations of Messrs.
Dease and Simpson in the polar regions, that such islands, when they run
aground, push before them large mounds of shingle and sand. It is
therefore probable that they often cause great alterations in the
arrangement of pliant and incoherent strata forming the upper part of
shoals or submerged banks, the inferior portions of the same remaining
unmoved. Or many of the complicated curvatures of these layers of loose
sand and gravel may have been due to another cause, the melting on the
spot of icebergs and coast ice in which successive deposits of pebbles,
sand, ice, snow, and mud, together with huge masses of rock fallen from
cliffs, may have become interstratified. Ice-islands so constituted
often capsize when afloat, and gravel once horizontal may have assumed,
before the associated ice was melted, an inclined or vertical position.
The packing of ice forced up on a coast may lead to similar derangement
in a frozen conglomerate of sand or shingle, and, as Mr. Trimmer has
suggested[130-A], alternate layers of earthy matter may have sunk
down slowly during the liquefaction of the intercalated ice, so as
to assume the most fantastic and anomalous positions, while the
aqueous strata below, and those afterwards thrown down above, may
be perfectly horizontal.
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