GEOLOGICAL AND PREHISTORIC TRAPS. 11
This evidence helps one to understand the larger-scale
conditions of the Essex coastal plateau. There is no longer
any question of seeking a correlation of these gravels with any
one of the Thames terraces, as I formerly attempted. We are
faced with a complex of channel deposits extending in time
from a very early stage of the Forest Bed, through the Glacial
Period, the Boyne Hill stage, and down to the very late Acheulean
channel of Upper Dovercourt.
Moreover, the "Forest Bed" of Tittle Oakley is itself a
channel deposit cut in the Red Crag which lies at the same level.
And if we note the other outliers of Crag at Mistley, Beaumont
and Walton, the Essex coastal plain is seen to conform at least
in part to the ancient plane of marine erosion of the Crag Sea,
the more remote extension of this Pliocene marine transgression
being represented by the Crag outlier at Stoke-by-Clare, the
Rothamsted discovery, the records of Crag bone at Thaxted
and the more recent find at Great Bardfield that was shown
to me a few years ago.
It is, therefore, theoretically possible that some of the local
gravels may be even older than the Tittle Oakley deposit.
Possibly an extended study of their erratic rocks might throw
some light upon their detailed classification, and I have com-
menced a systematic collection upon the following method.
I take 400 as a convenient and useful standard number of stones;
30 cms. in longer diameter as the lower limit of size (all smaller
than this being disregarded); and then I take a small sample
from every non-flint stone in the total of 400; and store these
for future comparison. I can say no more at present than
that there are great differences between the various local gravels.
The Crag Sea Floor and its Flaked Flints.—The fore-
going comments upon the floor of the Crag Sea inevitably suggest
the problem of the flaked flints that are found upon it ; this
introduces us to the most important and the most controversial
problem of prehistory.
One must first consider certain points in the evidences of
the sea-floor itself.
A few years ago I found at Runton the ramus of the lower
jaw of Elephas meridionalis (now in the British Museum) with
the last molar in place, under particularly interesting associations.