198 NOTES ON THE ANCIENT PHYSIOGRAPHY OF SOUTH ESSEX.
separating the basins of the Crouch and the Blackwater is a belt of
land, averaging little more than half-a-mile in breadth, and mainly
between 50 and 100 feet above the sea, only a few acres slightly
exceeding 100 feet. At St. Michael's Church the surface is 170 feet
above the sea, and there is a large area of equal or greater height
about Cold Norton. And on looking northward of this water-
parting where it is at its narrowest, we see that close to it, at
Latchingdon, rises the chief tributary of the Blackwater on its
southern side, which is known as Lawling Creek near its outfall
south of Osea Island. The low ground between Cold Norton and
St. Michael's Church, and the course of Lawling Creek, doubtless
mark the route of the ancient stream which flowed north or north-
west of Laindon Hill, Rayleigh, and Althorne, before it was super-
seded by the Thames.
When we remember that at a very recent time, geologically speak-
ing, England must have been united to the Continent, and that still
more recently our rivers must have flowed through land close to our
shores which is now sea, it becomes evident that we may gain many
useful hints as to the ancient physical geography of this district from
charts showing the channels and shoals of the adjacent sea. For,
though the position of channels and sandbanks is sure to become
more or less modified in time through the destruction of land by the
sea and other causes, yet there is likely to be a broad general per-
sistence in their arrangement. A chart of the estuary of the Thames
shows us what has been done by the planing-down action of the sea
on the soft clay, etc., of North Kent and Southern Essex, in forming
the broad flat known as the Maplin Sand, and in the still broader
submerged flat north of Sheppey and Herne Bay. One thing is
specially prominent, and that is the way in which the present
channels from the Nore Light eastward all range in a south-westerly
and north-easterly direction ; so that it would evidently be—in the
absence of lighthouses or lightships—a much simpler business to
guide a ship along one of these channels towards Amsterdam or
Denmark than to take it safely round the North Foreland to Dover
or Boulogne. For the course of the south-going ship must be taken
through irregular breaches in long and once probably continuous
belts of shoal and sandbank. And I think there can be little doubt
that the marine channels of the present estuary of the Thames mark,
in the main, the former course of the channels of that river and of
the Medway when they flowed through then-existing land many miles