ON THE LEA VALLEY. 3
valleys to their present depth, were flowing at some higher level,
often cap the London Clay at various heights. The lowest and
most recent of these river-deposits are those forming the marshes
bordering the Lea, in which the new reservoirs are being
excavated. Other gravel patches, which may be seen here and
there a few miles from the reservoirs, usually at greater heights
than the highest of the deposits mentioned, being unconnected
with any existing river system do not here concern us.
In the immediate neighbourhood of the new reservoirs, a
good example of the fragment of an old river deposit may be
seen on the northern slope of Higham Hill, about 150 yards
south-east of Higham Hill Ferry, and the same distance from
the southern edge of the more northerly of the two new
reservoirs. West of the Lea, the high road between Tottenham
and Edmonton is on old river gravel of less age and elevation
than that of Higham Hill. And while no bare London Clay is
anywhere visible between the marshes of the Lea and the
slightly older and more elevated gravel of Tottenham and Ed-
monton, there is a distinct belt of London Clay between the
marsh in which Banbury Reservoir is being excavated, and the
gravel and loam capping the northern edge of Higham Hill.
Another point of distinction between the gravel and loam of
Higham Hill, and of Walthamstow generally, and that of
Edmonton and Tottenham lies in the fact that they appear to
belong to two different rivers, the first-named to the Thames,
the latter to the Lea. At the present day we naturally consider
ourselves in the valley of the Lea four or five miles south of
Higham Hill. But examination of the Geological Survey Map
of the district showing the distribution of the river-deposits
makes it evident that the Thames, at one time, both above and
below London, took its course some miles north of its present
channel. And that the gravel of Stamford Hill, Higham Hill,
and Walthamstow was formed in all probability by the Thames,
when flowing in ancient times in a more northerly and a more
elevated channel than it now does.
Before descending from Higham Hill to the Marshes in
which the reservoirs are being excavated it may be well to note
the nature of the more ancient river-deposits capping the hill.
They consist of gravel covered more or less irregularly by loam,