THE ESSEX FIELD CLUB.
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formation, though he thought that some of the Hertfordshire pebble-gravel, which
is coloured with the same tint on the map, may be marine. In his opinion we have
in this instance merely debris of the neighbouring more massive beds of pebbles,
with a certain admixture of foreign material.
Mr. Woodward expressed his agreement with the explanation given by Mr.
Monckton. When engaged in 1871, together with his colleague, Mr. F. J. Bennett,
in mapping the geology of the country near Brentwood, they were often much
perplexed with the many deposits of gravel, for it was most difficult to correlate
them, or determine their respective ages. The deposits generally grouped as
"Pebble Gravel" were those characterized by an abundance of flint and quartz
pebbles, and they were to be distinguished from the so-called Middle Glacial Gravels,
by the absence of brown quartzites and of the derived Jurassic fossils, to be met
with in the glacial drifts. The "Pebble Gravel" was in the main pre-glacial, so
far as Essex and Hertfordshire are concerned, but there was no evidence to suggest
that it was pliocene. With regard to this gravel at Warley, Mr. Woodward
admitted it was very doubtful if it could be classed as of the age of the main mass
of the "Pebble Gravel" (i.e. "Gravel of the Higher Plain" of Professor Hughes),
for it appeared to be due simply to local denudation of the Bagshot Pebble-beds.
This might have taken place during glacial times, for Boulder Clay has been met
with on the high grounds at Brentwood ; and then foreign materials might have
been introduced.
Perhaps the most difficult question, and one indeed which puzzled Mr. Wood,
was, What was the source of the quartz pebbles ? The question cannot be definitely
answered, although it is possible that the Millstone Grit, like that of Kinder Scout,
may have contributed to the supply.
Attention was drawn to the fact that here, as well as in other pits visited, the
pebbles for some depth occur mostly with their longer axes pointing downwards.
Mr. Woodward remarked on the explanation given by the Rev. O. Fisher
(Quarterly Journ : Geol: Soc :, vol. xxii, p. 553), viz., that pebbles might attain such
a position in sinking through a muddy deposit. In several instances the beds are
distinctly contorted, so that direct glacial action, and perhaps also the influence of
frost and thaw may have combined to produce the result. Mr. Holmes remarked
that in some places the Oldhaven pebble-beds present the same features.
Proceeding in a westerly direction the party examined several pits opened in
pebbly gravel at the northern end of Holdens Wood, and a little south-west of
Warley Barracks.
Here the deposit consists, as before, mainly of flint pebbles, whilst quartz is
found but rarely in small pea-like grains. Sub-angular flints are also met with.
About 10 feet of gravel is shown resting in places on yellow sand of Bagshot
character. Mr. Woodward believed that the lower beds, for a foot or two
(in places), were undisturbed Bagshot pebble-beds, and in them, here and
there, a thin impersistent seam of White Clay was observable. He remarked on
the section formerly exposed near Langtons, on the eastern side of South Weald
Park, where beneath 6 feet of the more or less disturbed pebbly gravel, with
quartz, etc., there was exposed about 15 feet of the Bagshot pebble-beds.2 It
was this section, which he had seen in 1870, in company with Mr. S. V. Wood, jun.,
and later on with Mr. Whitaker, that led to the conclusion that the pebble beds
were of Bagshot age, a view advanced in 1864 by Mr. Wood. Unfortunately the
section is now obscured, so that although the party proceeded to the spot they were
2 See Whitaker's "Geology of the London Basin," p. 324.