196 NOTES ON THE ANCIENT PHYSIOGRAPHY OF SOUTH ESSEX.
are only visible on close inspection. Consequently, a glance at one
of the latter maps gives us much less information about the physical
geography of the district than would be obtainable either from the
geological map, or from the shaded maps of the older Ordnance
Survey. It is necessary, therefore, to colour or shade the New
Ordnance map if we wish to get the most complete knowledge of
the present shape of the ground, and the trouble involved in doing
so is amply repaid by the result attained. We then see revealed very
strikingly the existence of a broad continuous tract of low ground
from Romford eastward to the Blackwater below Maldon. This low
ground is bounded on the north and west by a perfectly continuous
tract of higher land, towards the edge of which are Warley, Billericay,
Woodham Ferris, and Maldon. South-east of the belt of lowland we
see another belt of high ground, ranging in a direction nearly parallel
with that first mentioned, but not so continuous, from Laindon Hill
to Rayleigh and Canewdon, and thence, north of the Crouch, to
Althorne and Mayland. And, though the continuity of this high
ground is now broken at Pitsea, the present shape of the surface there,
and the fact that the Thames has there swept away all its own
older deposits, and with them probably much of the higher ground,
leaving in their place only comparatively modern alluvium, point to
the conclusion that the high ground of Laindon Hill was continuous
with that of Hadleigh and Rayleigh down to a geologically recent
period.
The belt of lowland does not now show a uniform slope from
Warley and Laindon to the Blackwater ; but that is, as we shall see,
the result of denudation, which, at a period much later than that of
the superseding of the Romford river by the Thames, has given rise
to the streams known as the Mardyke and the Crouch. I think
there can scarcely be any doubt that at river at one time flowed
through the belt of lowland from the neighbourhood of Romford
eastward to the Blackwater below Maldon, and that the old silted-up
stream-course seen at Romford was probably a portion of it. And
that this river ceased to exist when the Thames eroded away the
high ground between its own valley and that of the Romford stream,
tapped its water supply, and diverted the drainage of the district."
3 West of Romford, the ancient representatives of the Hoding and the Lea probably united
with the Romford stream and had their outfall in the valley of the Blackwater below Maldon before
the Thames altered the course of the drainage. But only east of Romford can we get any evi-
dence as to the course of what I have termed the Romford stream. West of that town the
Thames Valley deposits occupy- the ground, and prevent all knowledge of the earlier physiography
of the district.