54
THE ESSEX NATURALIST.
alluvial plain is formed in the bottom of the valleys, which in-
creases in width until, north of Ickleton, it merges into the
flat lands of Cambridgeshire.
The general geological structure may be summarized as
Boulder Clay above the 300ft. contour line, Chalk on the hill
slopes, and Alluvium in the valley bottoms below the spring
heads. The valley bottoms are fringed at intervals by gravel
terraces of varying width, and exposures of gravel occur here and
there on the valley slopes where the mid-glacial Gravels outcrop
between the Chalk and the Boulder Clay. Small exposures of
gravel and loam also occasionally occur on the tops of the
ridges. The Chalk slopes are usually covered with a rainwash
which is often of a clay-like consistency, but in steep places the
soil may consist almost entirely of finely powdered chalk.
It seems probable that in Neolithic times the clay hill-tops
were covered with damp oak-ash woodland (14), the hollows
in its recesses being occupied by a swamp flora with numerous
ponds and small lakes. The Chalk slopes were clad with grass
or scrub land with a flora corresponding to that of the New-
market and Royston Heaths (14), but it should be noted that
the sporadic occurrence of typical beech-wood plants, such
as the White Helleborine (Cephalanthera grandiflora), points
to a possible northern extension of the primitive beech wood
of the Chilterns. The valley bottoms were choked with a swamp
or wet alder wood flora and there are indications that at New-
port, Wenden and Saffron Walden the side valleys below the
spring heads were occupied by either incipient fens or shallow
lakes.
THE REMAINS OF NEOLITHIC MAN IN THE CAM
VALLEY.
Neolithic earthworks in the area are restricted to a few
doubtful examples only.
In Grimsditch Wood (2), about 11/2 mile N.N.E. of Saffron
Walden Church, there is a rampart and ditch with a cigar-shaped
mound enclosed in the north corner. It is associated with an
implementiferous area and is possibly a Neolithic camp.
The lynchetts or cultivation terraces at Ickleton (3) are
associated with worked flints, which occur on the flats of