172
THE ESSEX NATURALIST.
The Winter Hill Terrace (150 to 180)* [Wooldridge, 1938,
etc.].—This is the oldest terrace subsequent to the diversion of
the Thames, and thus related to the present valley near London.
Wooldridge, to whom its recognition is due, considers that this
terrace is associated with the Glacial outwash gravels. This
seems reasonable, but must await confirmation.
The Thames Terraces.—There have been differences of
opinion associated with confusion of nomenclature in the classi-
fication of the Thames terraces. The Geological Survey have
adopted the scheme, 1. Boyn Hill [= 100-ft.]. 2. Taplow [ =
50-ft.]. 3. Flood Plain. This is well adapted to mapping, but
I shall endeavour to show that it brings together deposits of
different age, and separates deposits of the same age.
I can best explain this point of view by considering the effect
of an emergence of 50 feet at the present time. The result would
be the addition of another terrace, but this, while being a unit
of form to map, would be composite in date. It would include
1. The sub-Arctic Ponders End stage (q.v.). 2. The cool
temperate Buried Channel deposits (q.v.), both of which are
Pleistocene. 3 A Holocene sequence of minor climatic fluctua-
tions covering some 10,000 years.
I think there is good evidence that we must take a similar
view of the complexities of the older terraces, and that we
cannot take them as units of date, or in a straight sequence of
relative level
The Dartford Heath Stage (90-130).—This gravel contains
many Glacial derivatives. It is well seen at Dartford Heath,
and the other gravels that I associate with it consist mainly of
outliers, or remnants of sheets of which the greater part has been
swept away. I identified a good example on Stamford Hill
some years ago, and other remnants occur in S. Essex. I believe
that the name site of the Boyn Hill terrace [Treacher, 1909]
belongs to this group, but that many of the gravels mapped under
the same name are later.
The "zone fossil" is a primitive flint industry, the earliest
Lower Paleolithic, but whether one calls it Early Acheulian,
Chellian, Abbevillian or Strepyan, is more a matter of terminology
than of fact. Much still remains obscure, but I believe the
archaic variety of Elephas antiquus belongs to this stage.
Hornchurch.—It will be remembered that T. V. Holmes
[1892] recorded Boulder Clay below the 100-foot terrace in a
railway cutting. The gravel is between 90 and 105 O.D. and the
base of the underlying Boulder Clay is below 80. The Romford
Memoir [1925] reproduces a photograph of a section on the
4 Range of level in feet O.D. (see note at end).