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The numbers actually employed vary from a few hundred to
several thousands at the larger factories.
SUPERFICIAL GEOLOGY
Geological formations occurring in the London Borough of
Greenwich are of two groups, namely, the "superficial deposits" and
the "solid formations". These are given below, seriatim, in descending
order and while this holds good for the area as a whole, the
complete sequence is not always met with for superficial deposits
may be non-existent, local arching of strata and subsequent denudation
of the higher parts may have brought to the surface lower
members of the succession and, in other cases, a stratum of the
sequence may be entirely absent, Where maximum and minimum
depths are stated, this implies a true variation of the thickness of the
beds in question and, with the exception of the superficial deposits,
is not to be ascribed to thinning due to erosion.
Superficial deposits in the Borough are distributed over the surface
of the "solid formations" and may be considered as being of (a)
"made" ground, (b) alluvium, and (c) gravel, the latter deposit being
of the Pleistocene or "drift" series. At some places these deposits fill
deep hollows in the surface of the "solid" attaining a maximum
thickness of about 70 feet and at others are arranged as banks. More
usually they form spreads of comparatively uniform thickness, or
remain caps to the higher ground. Situated below these are the "solid"
Eocene formations of Claygate, London, Blackheath and Woolwich
& Reading beds followed by that of Thanet Sand. Underlying the
whole Eocene strata is the Chalk or Cretaceous formation.
Superficial Deposits
Made—Made ground, consisting of artificial accumulations of
debris and dumped materials from excavations have been spread
over a number of areas of the district especially where the material
has been used to raise the surface level of alluvial areas to reduce
flooding in times of exceptionally high tides and heavy rainfall.
Alluvium—Such a term is applied to the deposits up to 30 feet in
depth forming the low-lying areas bordering the Thames and its
tributaries. Originally marshland, these areas are still liable to flood
should the river overflow its banks except where artificial means of
protection have been adopted.
Consisting of alternations of mud or silt, clay, shell marl, peat, sand
and gravel, any or all of which may be present, the deposits may lie
directly on "solid formations" or on banks of "river terrace gravel".
Alluvium components are subject to rapid changes in thicknesses and
often arranged in "lens-shaped" masses.