135
NOTES ON A MANGANIFEROUS SEAM IN THE
THAMES VALLEY DRIFT AT ILFORD,
ESSEX.
By J. P. JOHNSON.
The continued erection of houses on the site of the old
Uphall Brickyard has necessitated the opening of several new
pits for the supply of building material, since those described in
an earlier paper1 were filled in. As a rule the sections thus
exposed shew no additional features of interest and further back
attraction in that they have not yielded any fossils.2
However, there are exceptions to every rule and the follow-
ing section which is situated between the "Hunter," "Uphall"
and "Harvey Roads," is well worth noting :—
Fine Ochreous Gravel .. 4 ft.
Ochreous Sand .. .. 3 ft.
White Sand .. .. 1 ft
For between the gravel and sand, which pass into one
another, there is a lenticular seam coloured black with hydrated
oxide of manganese, which occurs in the amorphous form of
psilomelane, coating the grains and pebbles.
I took three samples from different parts of the seam with
the object of determining the percentage of manganese present.
Sample i. was estimated by my friend, Mr. W. G. Rumbold, to
contain 27 per cent. Sample ii., which was kindly analysed
by my friend Prof. Geo. Patchin, A.R.S.M., and by Mr. F. A.
Zurcher, yielded .975 per cent., while sample iii., which was
assayed by myself, contained only .68 per cent. All three
samples were assayed gravimetrically by the "basic acetate"
process, and very carefully checked by duplicate assays.
It will be seen that the results vary somewhat, but their
difference is not greater than might have been expected from the
nature of the deposit, because, since the psilomelane occurred
only as a film on the exterior of the pebbles and grains, the
sandy portions of the seam would naturally contain more
manganese than the pebbly portion.
1 J. P. Johnson, 'Additions to the Palaeolithic Fauna of the Uphall Brickyard, Ilford."
Essex Naturalist, vol. xi. (1900), pp. 209-215.
2 I have, however, obtained the greater part of a large hache which I have handed over
to the Essex Field Club's Museum at Stratford. It is very much abraded and is probably
derived from the high-level drift of this valley.