Lambeth Group is a stratigraphic group, a set of geological rock
strata in the London and
Hampshire Basins of southern England. It
comprises a complex of vertically and laterally varying gravels,
sands, silts and clays deposited between 56-55 million years before
present during the
Ypresian age (lower Eocene). It is found throughout
London Basin with a thickness between 10m and 30m and the
Hampshire Basin with a thickness between 50m and less than 25m.
Although this sequence only crops out on the edges of these basins,
the fact that the
Lambeth Group underlies some 25% of London at a
depth of less than 30m means the formation is of engineering interest
for tunnelling and foundations.
3 Stratigraphic relationship
The formation was first known as the Plastic
Clay by T. Webster in
1816 after the Argile plastique of
Georges Cuvier and A. Brongniart.
It was called the Mottled
Joseph Prestwich in 1846, but in
1853 he proposed the name Woolwich-and-Reading Beds to emphasise the
differing local aspects of the series. This name received widespread
usage, however, has in turn been recently deprecated in 1994 in favour
Lambeth Group by the
British Geological Survey
British Geological Survey to conform with
new standards and to allow scope for more detailed subdivisions.
Lambeth Group consists of three formations:
The Reading Formation, a series of lenticular mottled clays and sands,
here and there with pebbly beds and masses of fine sand converted into
sandstone. These beds are generally unfossiliferous. They are found in
the north and west portions of the
London Basin and in the Hampshire
The Woolwich Formation, grey clays and pale sands, often estuarine
shells comprise a very substsantial component and in places with a
well-marked oyster bed. At the base of the shell-bearing clays in
southeast London there are pebble beds and lignitic layers. The
Woolwich Formation occurs in west Kent, the east borders of Surrey,
the borders of east Kent, in south
Essex and at Newhaven in Sussex.
The Upnor Formation, consisting of light-coloured false-bedded sands
with marine fossils occurs in east Kent. Where it rests on the Thanet
beds it is an argillaceous greensand with rounded flint pebbles; where
it rests on the chalk it is more clayey and the flints are less
rounded and are green-coated.
Reading Formation appears on the coast at Studland Bay
and at other points inland. The
Hertfordshire puddingstone is a
well-known rock from near the base of the formation; it is a flint
pebbly conglomerate in a siliceous matrix. The fossils, estuarine,
freshwater and marine, include
Corbicula cuneiformis, C. tellinella,
Ostrea bellovacina, Viva parus lentus,
Planorbis hemistoma, Melania
Neritina globulus, and the remains of turtles,
crocodiles, sharks, birds (Gastornis) and the mammal Coryphodon.
Bricks, tiles and coarse pottery and occasionally firebricks have been
made from the clay beds in this formation.
Except in the
Hampshire Basin, the
Lambeth Group usually rests on the
Thanet Formation of the Montrose Group, but is found on the Chalk
Group near Bromley, Charlton, Hungerford,
Hertford and Reading. It is
usually covered by the Harwich Formation, the oldest formation of the
This article incorporates text from a publication now in
the public domain: Chisholm, Hugh, ed. (1911).
"Woolwich-and-Reading Beds". Encyclopædia Britannica. 28 (11th ed.).
Cambridge University Press. p. 819.
Hight, D.W., Ellison, R.A. & Page, D.P.; 2004: Engineering in the
Lambeth Group, Construction Industry Research and Information
Association, Report C583
Jackson, A.A.; 2008: Bedrock Geology UK South. An explanation of the
bedrock geology map of
England and Wales - 1:625,000 fifth edition,
British Geological Survey, ISBN