THE ESSEX FIELD CLUB. 11
the taper ends of the roots still remain. In either case the main lignite
cr peat deposit rests on this eroded surface and the lignite and also the
upper two feet of the old roots are penetrated by small reeds.
Over most of the area the erosion has been much greater, the sand
having been swept away almost to the top of the coarse ballast. Over
part of the base of this hollow, near the east end of the main Dock, a
curious gravel deposit was swept, composed of rounded flints (mainly
Reading Bed pebbles)and sand mixed with fine detrital black-wood material
and freshwater shells, largely comminuted. Evenly dispersed through
it are thousands of more or less burned flints, which from their flatfish
upper surface and general aspect appear to have resulted from a forest
fire; they are quite unlike the burnt flints, associated with cooking pots,
referred to later. On this gravelly and peaty material more detrital
wood and waterlogged trunks of trees were deposited, the trees often acting
as strainers and catching objects which easily floated such as fresh-water
snails and hazel nuts, which are often abundant. The number of large
pieces of decayed timber in this deposit is greater than at any other horizon,
and solid (i.e., not soft and sodden) tree-trunks are rare. In it an oyster
shell has been found, and at its base, at two spots, flint flakes of undoubted
human origin ; there is no trace of a land-surface at this horizon, indeed
it was obviously an eroded hollow full of water. Above it comes slimy
clay with many waterlogged sodden fragments of tree-trunks and a fair
number of undecayed trunks. If a sandy seam occurs in this, fresh-water
shells are abundant. Many small reeds grew in it, and these penetrate
the sodden trunks which were in the condition of "touchwood" when
they sank.
This clay gradually filled the hollow up, or nearly up, to the level of
the old surface, and the main lignite bed passes over both the sand and
the later mud continuously, and is everywhere crowded with reeds, showing
that it was entirely submerged. Not a trace of moss has been found in
this lignite. It is doubtful now if the pure lignite contains any shells;
but there are numerous lenticular seams of clay and silty sand within
the lignite, often accompanied by slight local erosion, and in these seams
fresh-water shells are abundant, and more than thirty species have been
obtained therefrom, which have been kindly determined by Mr. B. B.
Woodward.
The mud that succeeds above the main lignite contains a large amount
of twigs, small pieces of wood, and waterlogged decomposed pieces of
tree-trunks. The whole of the mud and lignite also contains, sporadically,
numerous trunks of trees, which are still undecomposed, and these often
have portions of their roots attached, as if they had been either blown
down, or let down by the undercutting of the banks upon which they
grew.
Several cross-sections of silted-up Creeks, cutting into the peat and
choked with clayey silt, may be seen on the faces of the excavations;
the largest of these is the old Ham Creek, which is stated to have been a
navigable channel up to late Mediaeval times.
Vivianite (blue phosphate of iron) occurs in the peat and the alluvial
clay, associated with the plant-remains.
Mediaeval pottery, associated with oysters, bones, burnt flints, and