PLEISTOCENE DEPOSITS IN BILLERICAY, ESSEX 173
in a coarse-grained sand matrix shot through with limonite and
goethite. The coarse fraction of the matrix was not compatible
with it having been derived from the underlying fine-grained
Bagshot Sands.
Fig. 4. The junction between pebble gravel and Eocene sands—Hambro
Hill (B) and Hockley road (A).
Possibly the most intriguing feature of the Gravel was the
variation in composition and angularity of the pebbles which
formed some 20 to 50 per cent by volume of the sediment when
traced along the outcrop. The best rounded by far were dark
grey to black flints closely resembling those occurring within the
pebbly Blackheath beds of south London. They were intermingled
with rounded but flatter, mottled grey and brown flints of un-
certain affinities. Among the angular pebbles a certain proportion
were undoubtedly physically disintegrated (? frost-shattered)
Blackheath and allied types. However, more interesting, were
haematite-red cherts (or jaspers), forming about 3 per cent of the
total pebble assemblage. The red colouring agent disseminated
through the chert appears to be primary and its origin does not
seem compatible with any primary or subsequent process known
to have affected Cretaceous or Tertiary chert- and flint-bearing
formations of southeastern England. Hence the provenance of
these pebbles remains obscure, an obscurity not really clarified
by the association with large, angular, cream-veneered flints which
clearly have been subject to minimal abrasion and may have had
a not too distant southern Chalk provenance.