THE PAST HISTORY OF THE FOREST OF ESSEX. 129
1900, we may well ask the reason for this continuous defores-
tation of the Boulder Clay, when it seems that the same atten-
tion could be profitably employed to the land already cleared.
The reason lies in the value of the Boulder Clay soil. The
value of each manor is given in Domesday, and it is at once
apparent that those manors within the Boulder Clay region
had the greatest value. A further proof can be found in the
distribution of mills in 1086. Although, as seen above, the
manors were less numerous on the Boulder Clay yet the same
region contained by far the greatest number of mills, and the
Great Survey indicates that they had further increased since
1066, whilst other regions showed corresponding decrease. It
is this desire to cultivate the better corn lands that supplies
the continuous urge towards their deforestation.
In the following mediaeval times direct evidence relating
to the Forest is mainly confined to legal literature whose value
will be dealt with later. It seems, however, that the final
clearing of the Boulder Clay forested area was the great achieve-
ment of the times. Bearing in mind the evidence of the Domes-
day "valets," and being aware that the bulk of the eastern
London Clay was already cleared, it seems apparent that any
relative increase in the assessment values of Boulder Clay
parishes would indicate further clearing in that region.
With this end in view successive lists of taxation assess-
ments were mapped for the parishes, the series of maps so ob-
tained being compared.6 The only possible method of con-
structing such maps was to find a percentage value obtainable
from a consideration of the assessment and total parish acreage.
We may assume that the parish areas remained substantially
the same throughout the period under review. Since, however,
the arable area within the Boulder Clay region was known to be
small in 1086, it was not surprising to see in the first assess-
ment (1238) that many of the Boulder Clay parishes had low
assessments, apparently indicating this small percentage of
arable land. It was, however, significant that the average
assessment of the Boulder Clay region was higher than that of
the London Clay, whilst the highest assessment figures only
obtained in the former area. Some indication of high land
values could be seen on the light soil strips, whilst assessment
6 Public Record Office Subsidy Rolls.