THE DRIFTS OF SOUTH-WESTERN ESSEX. 163
The figure is diagrammatic and not to scale, as one could not
otherwise indicate the relations of the deposits within the limits
of a page.
The Pebble Gravel is interstratified with sand, and definitely
in place and undisturbed as originally deposited. The con-
stituents will be found under that heading, and it is absolutely
without trace of glacial material. An interesting item is the
inclusion of 1 % of burnt flints, which are not merely red-stained
or "jasperized". flints, but have the true characters of burning
by forest or heath fires. These also occur at the Chigwell Lane
section. The gravel lies between the levels of 135 ft. and
145 ft. O.D., and when the overlying deposits are removed it is
seen to form a well-marked terrace with a surface of some 10 or
15 feet above the river.
The locally pre-Glacial gravels of the Roding Valley (Chigwell
Lane and Hallsford) are clearly related to the dissection of the
200-ft. platform and indicate that extensive erosion intervened
between that platform and the Great Eastern Glaciation.1
The "Romford River."—This is the name given by T. V.
Holmes [1894] to an extinct river of which he traced the valley
by Romford and Upminster, and thence between Billericay and
Rayleigh to the Crouch Estuary. The valley is in part mantled
by Boulder Clay and is probably a former course of the Roding.
There was probably another river in the position of the
Thames Estuary (one might call it the "Nore River") which cut
its way west and successively captured the rivers of N. Kent
and S. Essex.
The Diversion of the Thames.—Let us go back for a
moment to envisage the main theory of the Thames flowing by
the Hertford-Ware route, and ask : If this be true what diverted
the river from such a long established course to its present
estuary ?
The generally accepted view is that the advance of the ice of
the Great Eastern Glaciation blocked the way. It is supposed
with much reason that the ice filled-up the Hertford-Ware Valley,
and, spreading over Hertfordshire, forced the Thames to break
through south of the Epping Forest Ridge into either the "Nore
River" or the "Romford River" (q.v.). As the ice melted the
lower Lea Valley was also reversed from N. to S. and deepened
by the Glacial melt-waters. [Sherlock 1924, Wooldridge 1938,
etc.]
(To be continued.)
See also The Hallsford Loess (post).