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37
pany. A full description of the strata cut through in making this
well has been given in The Lancet (March 27th, pp. 902-3).
The Kent Waterworks Company derives all the water supplied
from deep wells; it is therefore of interest to note the geological
character of the district. The Company's area is bounded on the
north by the River Thames, and to the south it extends beyond
the North Downs. A diagram shows the arrangement of the
geological strata.
At the extreme south Westerham is on the lower greensand,
a formation which contains extremely good water, much less hard
than the water found in chalk formation. Passing northwards
there is next a narrow layer of gault, an almost impervious clay
formation; then farther northwards there is a narrow band of
upper greensand. Still farther northwards is the range of the
North Downs, which run in a direction nearly due east and west,
the eastern end running to the sea just south of Deal. In a
westerly direection the downs run just to the north of Reigate
and Dorking to Guildford, and from the west of Guildford
towards Farnham. Near Westerham, the crest of the chalk
escarpment is generally over 600 ft. above the sea level.
The ground falls from the crest sharply to the south;
towards the north and the north-east the slope is more gentle.
The diagram shows the position of two of the chalk wells, at
Orpington and Crayford, and the position of the river beds of the
Cray, the Darent, and the Thames.
On the North Downs there are patches of clay with flints and
loam. These patches are irregularly distributed. From Westerham
to Orpington the section shown in the diagram runs in a
north-north-easterly direction; from Orpington to Purfleet the
section runs in a north-easterly direction. Between Orpington
and the line of the London, Chatham, and Dover Railway there
are springs. There are patches of lower tertiary beds between
this point and Crayford, which is on the chalk.
The depth of the level of water in the chalk varies. For
example, at the present time the level of the well at Orpington is
about 60 ft. below the surface of the ground. In a dry summer
the level has been as low as 90 ft. below the surface. In