178
THE ESSEX NATURALIST.
The constituents are :—C, Lower Greensand Chert ; F,
relatively fresh flint nodules ; Fs, relatively fresh sub-angular
flint ; W, flints showing the effects of prolonged weathering
before inclusion in the gravels. ; T, Tertiary flint pebbles ; Q,
quartz ; V, various rocks, such as Sarsen, grit, lydian-stone, etc. ;
B, Bunter pebbles ; G, Glacial erratics, other than flint. The
groups to which a star is placed were not separately classified.
The plus sign indicates that the frequency is less than one-fourth
of 1 % ; two dots, extreme rarity ; a nought, none found.
The sites 4 to 10 are from my own counting of stones, not
less than one inch in shorter diameter; I usually examine 400 at a
time, dug from the undisturbed deposit, and bring home a broken
sample of every non-flint stone. If a smaller sized stone were
taken this would make little difference except in increasing the
quartz content in certain cases, notably in 5, and less in 6 ; this
was probably done by Prestwich. Small quartz grades into sand
which is too ubiquitous to have any significance.
The range of level given in this paper refers to the usual
lowest base level and the usual highest surface level and not to the
thickness of the deposits.
REFERENCES
With indication of relevant subject-matter.
1880. Spurrell, F. C. J. Levallois working site, Crayford. Q.J.G.S.,
vol. xxxvi, p. 544.
1889. Whitaker, W. Geology of London.
1890. Prestwich, J. Westleton Beds (Pebble Gravel), Southern Drift, etc.
Q.J.G.S., vol. xlvi, pp. 84-181.
1892. Holmes, T. V. Boulder Clay under 100-ft. Terrace. Q.J.G.S.,
vol. xlviii, p. 365.
1894 . -----------. As above, and "Romford River." Q.J.G.S., vol. 1,
p. 443.
1894. Smith, W. G. "Man the Primeval Savage."
1900. Hinton, M. A. C. Wanstead and Ilford. P.G.A., vol. xvi, p. 271.
1901. -----------and Kennard, A. S. Grays Thurrock, E.N., vol. xi, p. 336.
1905. -----------. Lower Thames. P.G.A., vol. xix, p. 76.
1905. -----------. Grays Thurrock. E.N., vol. xv, p. 56.
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1912. -----------. Ponders End, etc. Q.J.G.S., vol. lxviii, p. 213.
1912. Chandler, R. H., and Leach, A. L. Erith. P.G.A., vol. xxiii,
p. 183.
1912. Sherlock, R. L., and Noble, A. H. Course of the Thames.
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