156 THE ESSEX NATURALIST.
In post-Pleistocene times a gradual intermittent depression,
affecting the southern part of Britain and the adjacent shores
of the Continent, caused the gradual disappearance of the plain
which previously occupied the position of the North Sea and the
final severance of Britain from the Continent. Land-bridges,
more or less interrupted, persisted for a time and were utilized
by pioneers with Mesolithic cultures, Maglemose and Danubian
immigrants, settlers from the Baltic with pottery of Peterborough-
Mortlake type, the megalith builders of the Medway Valley and
the Beaker Folk. The Thames acquired a gradually widening
estuary; the old right bank disappeared by erosion from sea
and river side; new rivers drained the Essex plateau. The
depression ceased at the junction of the Neolithic and Bronze
Ages, the terminal stages being indicated by the "Submerged
Forest Belt" and the "Lyonesse Surface" of Mr. S. Hazzledine
Warren. It was resumed in this area during the Roman period.
In the Bronze Age the boundaries of our area of South-East
Essex were: North, the Crouch; South, a narrower Thames
Estuary, fringed with low lands represented by Southend Flat,
Canvey Island and adjacent marshland; West, a low range of
hills of London Clay, capped with Bagshot Beds, extending
from Hadleigh to Hockley; in these arose the Prittle Brook and
branches of the Rochford River, which cut through the gravel
belt and united to form the Roach, an affluent of the Crouch;
East, remains of submerged lands, salt-water swamps inter-
sected by estuaries and swept by tidal water.
The surface soil was mainly London Clay, loams and ir-
regular beds of brick-earth. Above tidal influence it supported
an almost impenetrable oak forest, with undergrowth of sloe and
hazel and thickets of hawthorn and bramble; intersected by
streams bordered with willow and alder, with meres and fresh-
water swamps in the valleys [32]. Two areas only were free
from heavy forest growth: (a) Bagshot sands, on the western
hills, covered by heath and light birch-woods; (b) Pleistocene
gravel patches, remains of the river terraces, with open tree
growth and light scrub. These areas alone could be cleared
without much labour for the erection of huts and formation of
trackways; on them water was obtained easily from springs
and shallow weils; they were the only sites suitable for settlement
and all the evidences of prehistoric man in this area are found