144 THE ESSEX NATURALIST.
at a red heat, with clue admission of air to burn off carbonaceous
matter and fully oxidise the iron present, a lake-red product is
formed indistinguishable from that of the red "floor" itself.
The relation between the various products is best expressed
diagrammatically. Thus—
It is this identity of composition that exists between the
sandy loam, red earth and briquetage that perhaps offers an
explanation of the enormous mass of burnt red earth found on
the Red-hill sites. If clay is heated above a certain critical
temperature it is dehydrated and loses its plastic properties; fires
lit anywhere on the site, as one envisages it, whether for the
firing of pots, the evaporation of sea-water, or for domestic
purposes in general would bake the soil beneath and render it
non-plastic; under the kiln itself the baking process would
proceed further and a "red floor" would result.5
A notable proportion of the burnt earth on the Canvey sites
is also accounted for by disintegrated crude red ware (small
fragments of 1 to 5 mm. diameter) amounting in some samples to
over 35 per cent. of the burnt earth material; burnt earth of
similar character was found at Canewdon.
Looking to the fact that what are called "Red-Hills" are in
reality not hills at all, but rather low mounds or level spaces
indistinguishable from other marsh mounds of a flat description,
may it not be possible that the Canvey sites were developed not
by the excavation of raw material on a neighbouring site and its
transport to a central area for industrial utilization, but rather
by a process of "quarrying" at a bank face in a manner analogous
to that still in use at brickfields of the older type?
5 See paper by J. B. Calkin, "Antiq. Journ." xv, p. 421. "Construction and Working
of a Rom-Brit. Kiln at Corfe Mullen."