166
THE ESSEX NATURALIST
sandstone bearing no resemblance to the Bagshots of Essex. Even
more rarely there were very large nodular flints up to 20 cm in
diameter, which showed little indication of abrasion. It should be
added that no examples of Pinhole Rag were found, nor were any
pebbles of Bunter type. The matrix is characterised by well
rounded quartz grains and most typifies the deposit, distinguish-
Fig. 2. Grain size distribution of the Pebble Gravel.
ing it from other local gravels. (Ovoid flints of a great variety of
colours occur in most of the Pleistocene deposits of the area
though not normally in the abundance found in the Pebble
Gravel). Generally, the sandy matrix is composed predominantly
of well-rounded near-spherical grains of quartz, quartzite, vein
quartz, fine-grained sandstone, goethite and occasional flint. All
of these are coated with a film of goethite sometimes mixed with
an altered fibrous mineral, possibly glauconite. The well-rounded
grains are accompanied by less well-rounded and even some
angular quartz and quartzite grains. When cleaned of their
goethite coatings nearly all the grains are highly polished and
some quartzes are water clear. Some parts of the matrix are more
clay-rich and in other parts the pebbles are in aggregates—
coated and joined with a grey or white sticky clay—the whole
being set in the more normal sand. The finest part of the matrix