194 NOTES ON THE ANCIENT PHYSIOGRAPHY OF SOUTH ESSEX.
yet that it appears here and there at lesser elevations in the valleys
of the Roding and the Ingrebourne, as well as on the new railway
at Hornchurch and Romford. And that it descends to still lower
levels in the valleys of the various streams around Chelmsford, which
unite to form the Blackwater below that town. It was evident,
therefore, that the valleys of the streams just mentioned must have
been excavated to some extent before the deposition of the Boulder
Clay. And that they belonged to another system than that of the
present Thames, the oldest gravel of which had been found in the
district around Romford, overlying the Boulder Clay.
As regards the course taken by the stream, a fragment of whose
silted-up bed was seen at Romford, I pointed out that it flowed
probably between Warley, Billericay, and Maldon, on the north and
west, and Laindon (or Langdon) Hill, Rayleigh, and Althorne, on
the south and east, into the valley of the Blackwater below Maldon.
I propose to consider more fully on this occasion the evidence
bearing upon the ancient river-systems of South Essex.
If we look at the map of the Geological Survey, with the view of
learning something about the physiography of South Essex from the
distribution of the various geological formations found therein, we
obtain the following information : We find that the Bagshot outliers,
certain high-level gravels, and the Glacial gravel and Boulder Clay
(all beds to be found only at comparatively high levels) exist mainly
north of a line drawn through Chigwell to Havering-atte-Bower and
thence about two miles south of Brentwood and Billericay through
Woodham Ferris to Maldon. South and east of that line we have
a belt of country the surface of which consists of London Clay,
above which, towards its southern margin, rise outlying patches of
Bagshot Beds and high-lying gravel at Laindon Hill and around
Rayleigh. Then, mainly south of a line drawn from Barking Side
through Romford, N. Ockenden, Stanford-le-hope, and Pitsea, lie
the gravel, brick-earth, and alluvium of the Thames Valley ; while
east and north-east of Pitsea, from Leigh and Southend to the
mouth of the Blackwater at Bradwell, similar beds of gravel, brick-
earth, and alluvium occupy a considerable belt of ground between
Rochford, Canewdon, Burnham, Southminster, Tillingham, and
Bradwell on the west, and the sea on the east.
From the distribution of these various deposits the geologist
would rightly infer that there was high ground at and north of
Havering-atte-Bower, Brentwood, Billericay, Woodham Ferris, and