192 THE ESSEX FIELD CLUB.
THE ESSEX FIELD CLUB.
EXCURSION TO CHARLTON, KENT.
Saturday, June 24th, 1899.
On this afternoon, at the invitation of the Croydon Natural History
Society, Geological Section (of which our former member, Mr. N. F. Robarts,
is Hon. Secretary), a joint meeting of the two societies was held at Charlton,
near Woolwich, and was well attended by members of both Clubs. Dr. H.
Franklin Parsons, F.G.S., and Mr. Robarts were the Conductors, while Mr.
W. H. Dalton, F.G.S., Mr. T. V. Holmes, F.G.S., and Mr. W. Whitaker,
F.R.S., also aided in giving short "demonstrations in the field." We are
indebted to the courtesy of Dr. Parsons for the following excellent account of
the geological observations made : —
The chief interest of the excursion was geological, its objective being a
large sandpit about about half a mile east of the station, permission to visit
this pit having been kindly given by the proprietor, Mr. Gilbert. This pit is
at the N.W. corner of a grassy hill commanding a fine view of the Thames.
On the flat summit of this hill are the remains of an ancient (? Roman) Camp,
but the entrenchments have been much encroached on and destroyed by the
excavations which have been subsequently made on the sides of the hill. This
is especially the case on the east side, where the wall of the camp has been
entirely destroyed by a very large excavation, now disused and converted into
a recreation ground for Woolwich. The numerous large excavations, now
mostly disused, which exist along the ridge of hill overlooking the Thames,
were made in former times, chiefly for the purpose of digging sand and gravel
as ballast for ships returning to the Tyne and other northern ports after
having brought cargoes of coal to London. The digging of sand and gravel
for this purpose has now been superseded by the use of water ballast. Mr.
Gilbert's pit is worked chiefly for the purpose of obtaining moulding sand for
foundry use. It exhibits a fine Oldhaven section of the strata from the
Oldhaven Pebble bed to the Upper Chalk inclusive. The Upper Chalk is
seen in the bottom of the pit, and a few specimens of Inoceramus and the
commoner Sea-urchins were obtained from it. At the junction of the Chalk
with the superjacent Thanet Sand is a bed of green-coated unworn flints.
This bed ranges in thickness from 6 to 18 inches or more, being thicker where
it fills up hollows in the surface of the chalk beneath. Above this is the
Thanet Sand, for which the pit is worked. This bed is some 30 to 40 feet
thick. The lowermost portion, 7 feet thick, and locally called "blackfoot," is
of a somewhat loamy nature, and is valuable for moulds for brass castings,
The next 12 feet above this consist of larger-grained and less cohesive sand,
better adapted for mould for iron castings. The upper part of the Thanet
Sand is a sharp white sand. In the lower part of the pit a pocket was
observed in the sand containing a current-bedded infilling with clayey
partings. Above the Thanet Sand, and separated from it by a pebble layer,
come the Woolwich beds, some 20 feet in thickness ; these consist of an
alternating series of sands with ferruginous concretions, shelly clays and
pebble beds. These beds dip and thin out to the west on the slope of the
hill on that side, this being due to their having slid down the hill and become
hereby drawn out. At the top of the pit the Oldhaven pebble beds are seen.