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are exposed around Woolwich, Charlton, Greenwich and north of
Lewisham, while at Plumstead Marshes the eroded beds are overlain
by superficial deposits.
Normally up to 55 feet thick, the beds reach a maximum thickness
in the south east of the area.
Chalk—This formation, almost entirely composed of soft, white
limestone with flints, is present everywhere in the area underlying
the Eocene strata except when it comes to the surface at Woolwich
and at the Greenwich Fault on both sides of the River Ravensbourne
in the vicinity of the Blackheath Hill, Brookmill Road and
Loampit Vale areas
Its thickness, which can be from 550 to 740 feet, is subject to
considerable variation due to pre-Eocene erosion, but the formation
is usually divided into Upper, Middle and Lower chalk beds, and
these are often sub-divided in accordance with the types and species
of fossils found therein.
The accompanying sketch map gives a clearer picture of the
various geological formations found within the Borough.