364 PLEISTOCENE GEOLOGY OF THE THAMES VALLEY.
There is one valley to which it is necessary to refer in some
detail, namely, that occurring to the west of Hangman's Wood.
Its direction is north and south, its southern end opening out into
the lower ground formed by the Brickearth and Alluvium border-
ing the Thames. Its early origin is somewhat obscure owing to
the fact that it has been much modified by the Thames in
Pleistocene times. This modification has tended to increase
both its width and its depth, but more especially the latter, the
result being that the High Terrace Gravel which formed its
floor has been swept out together with part of the underlying
Thanet Sand. Slightly to the west of the mouth of this valley a
good section is to be seen exposed in the "Globe" brickfield,
near Little Thurrock. This section shows how this deepening
was accomplished. Here the Thanet Sand has had its surface
Fig. 4. Section in the "Globe Works" Pit east of Grays. 1. Brickearth ;
2, Brickearth and Gravel Interstratified (Middle Terrace Series) ; 3, Gravel
and Sand washed down from Valley to the North (High Terrace Series
derived) ; 4, Thanet Sand.
eroded by the mechanical process of gravel being swept over it,
and upon this eroded surface a mixture of well stratified detritus
derived from the High Terrace Gravel and the Thanet Sand
reposes, the dip of which is to the south the angle of inclination
being similar to that of the floor of the valley. Upon this re-
arranged material the Middle Terrace Brickearths have been
laid. It is, therefore, clear that the deepening and widening of
this valley took place during the time which ensued between the
end of the High Terrace stage and the deposition of the earliest
sediments of the Middle Terrace (Fig. 4).
From these facts it is safe, in our opinion, to regard the
valleys referred to as being the result of the solvent action of