NOTES ON ESSEX GEOLOGY.
267
of Westleton, etc. In the case of Clacton the gravel may be
still newer.
Our nearer neighbours, the gravels of High Beach and
Jacks Hill, I have practically classed, as Prestwich does, with
the Westleton Beds, although not using that name, but being
content with "pebble-gravel," on the Geological Survey Map
1 N.W.
The conclusions drawn as to the relation of the Westleton
Beds to the Glacial Drift of the Thames Valley depend so largely
on the correctness of the classification, as given above, that I
think we should be cautious in accepting them until we can be
more certain, and certainty in the classification of gravels seems
often to be far off.
Part iii. of this set of papers treats of the Hill Gravels of the
Warley and Brentwood Groups, including those of Rayleigh
and Langdon Hill. Whilst saying that "there can be no doubt
of the Pre-Glacial age," the author hesitates to include them
with his Southern Drift (to which this part chiefly refers), though
he does not class them as Westleton Beds.2 I cannot but think
that not only have some of these gravels "the essential character
of a Bagshot pebble-bed," but that they are such, and not
Pre-Glacial Drift.
The relation of these various beds to the erosion of the
Weald is really beyond our Essex view ; but in the genesis of
the Thames we are concerned (though topographically more
with its latter end). The author (who thinks that this origin
dates "from late Pre-Glacial or early Pleistocene times"),
well says : "This is a branch of geology which opens some very
large and interesting problems. . . . Owing to the vast erosion of
the surface, the evidence respecting the older Drifts is generally
very fragmentary, and has often been entirely swept away.
Some speculation is therefore unavoidable, though it is essential
that the consequences that may result from hypothetical assump-
tions should be in harmony with the results of observation."
(pp. 179, 177).
In this year I gave some details of the deep channel of
Drift in the head-part of the valley of the Cam, which channel
had been proved to a depth of 340 feet, without reaching the
bottom, carrying the Drift to considerably below sea-level.3
2 Quart. Journ. Geol. Soc., Vol. xlvi., pp. 162-165. 177.
3 Quart. Journ. Geol. Soc. , Vol. xlvi., pp. 333-340.