226
ADDITIONAL GEOLOGICAL NOTES
Company at Walthamstow in 1868-69, south of those now being
made. The sections in the river deposits of Walthamstow
Marshes, closely resembled, as might be expected, those within
the newer and more northerly reservoirs. And Dr. Woodward
adds, that while the depth of the general floor within the
reservoirs nowhere exceeded 10 feet, "the trenches made for the
'puddled walls' in the centre of the artificial embankments went
down to a depth of 20 to 24 ft."
The details preserved by Messrs. Sharrock and Spencer
show a very much greater amount of variation as to the depth of
the London-clay beneath the river deposits in the new reservoirs,
than has been met with elsewhere in the district. At the
neighbouring spots already mentioned the depth varied from
10 to 24 ft. In the more northerly of the new reservoirs, the
"Banbury Reservoir," the London-clay was generally reached
in the puddle-trench on its eastern border (near the edge of the
marsh) at depths of from eight to nine feet. At other parts of
the reservoir boundary the depth was greater, the variations
being, however, very gradual, and the greatest depth reached
being 26 ft. at the most westerly point of the reservoir, a few
yards due east of the rifle butts. In the boundary bank of the
southern, or Lockwood, reservoir the variations were much
greater and more sudden. Starting from its southern end, I was
informed that a few yards west of the old channel of the
Lea,2 London-clay was found at a depth of 13 ft., and at 25 ft.
at a similar distance east of it. Proceeding in a northerly
direction, along the western side, as far as Stonebridge Lock,
the greatest depth was 23 ft. and was met with close to the Lock.
Along the eastern side London-clay was deepest at a point about
due west of the northern end of "Low Maynard Reservoir,"
being there 36 ft. below the surface. The average on the
eastern side was from 20 to 25 ft., or very nearly the same as
that of the western side from Stonebridge Lock southward.
But on the western side, from Stonebridge Lock to the north-
western end of the reservoir, the London-clay gradually becomes
deeper, and was found to he, at the north-western corner, 57 ft.
below the surface of the marsh. Then, 60 or 70 yards east of
that point, in the northern boundary, the clay was only 15 ft.
below.
2 See Map, Essex Naturalist, vol, xii., p. 2 (1901).