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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.