THE PAST HISTORY OF THE FOREST OF ESSEX. 117
varying climatic conditions result in important vegetational
differences. The coastal rainfall is very low indeed, being the
lowest in the British Isles. The effect on vegetation of onshore
winds of no inconsiderable force cannot be ignored. These
varying climatic factors broadly divide the county into two
regions—a western inland region with heavier rainfall and
less violent winds, an eastern coastal zone with lighter rainfall
and greater windiness—the latter region being more inimical
to woodland growth.
Variability of these climatic factors would not, however,
greatly affect the vegetation of the light soils—they being
naturally lightly wooded, but the adverse coastal climate would
result in a scantier woodland covering on the clay-lands.
Any definite division of the two climatic regions must
necessarily be arbitrary, but the divisions falling to either side
of the 23 ins.: isohyet seem not without significance in the
vegetational history of the county. This rainfall line skirts
the low Tendring plateau passing westward to encircle the
district around Colchester, from whence it trends south-westwards
towards Chelmsford. After encircling the Chelmsford district
it continues eastward to take in the high land by Danbury and
then curves southwestwards along the Stock-Billericay ridge
to meet the county boundary at the Thames near Rainham.
Outliers of the 23 ins. isohyet occur near the higher land of
Hockley and Dengie.
The arbitrary division includes the entire Boulder Clay
district within the region favourable to woodland, but cuts
the London Clay into western and eastern regions—the latter
having a climate unfavourable to forest growth owing to its
low rainfall and the prevalence of onshore winds.
This division enables us to postulate four natural wood-
land types in Essex—a scanty woodland growth on the three
light soil belts and a slightly heavier type of woodland on the
eastern London Clay. The Boulder Clay land to the north
of the county would carry a still heavier forest growth, whilst
dense undergrown woods would obtain on the western London
Clay if the natural vegetation were allowed to flourish. As
few changes of a nature likely to affect these vegetational
regions have occurred in Essex since the close of Neolithic
times, it seems reasonable to urge that the forest of Essex