round, on the inner sides near the bottom. My son Horace protracted
these measurements on paper; and though the curved line representing the
thickness of the mould was extremely irregular, yet in both diagrams it
could be seen to be thicker on the north-eastern side than elsewhere.
When a mean of all the measurements in both the trenches was laid down
and the line smoothed, it was obvious that the mould was thickest in the
quarter of the circle between north-west and north-east; and thinnest in
the quarter between south-east and south-west, especially at this latter
point. Besides the foregoing measurements, six others were taken near
together in one of the circular trenches, on the north-east side; and the
mould here had a mean thickness of 2.29 inches; while the mean of six
other measurements on the south-west side was only 1.46 inches. These
observations indicate that the castings had been blown by the south-west
winds from the circular enclosed space into the trench on the north-east
side; but many more measurements in other analogous cases would be
requisite for a trustworthy result.
The amount of fine earth brought to the surface under the form of
castings, and afterwards transported by the winds accompanied by rain, or
that which flows and rolls down an inclined surface, no doubt is small in
the course of a few scores of years; for otherwise all the inequalities
in our pasture fields would be smoothed within a much shorter period than
appears to be the case. But the amount which is thus transported in the
course of thousands of years cannot fail to be considerable and deserves
attention. E. de Beaumont looks at the vegetable mould which everywhere
covers the land as a fixed line, from which the amount of denudation may
be measured. {265} He ignores the continued formation of fresh mould by
the disintegration of the underlying rocks and fragments of rock; and it
is curious to find how much more philosophical were the views maintained
long ago, by Playfair, who, in 1802, wrote, In the permanence of a coat
of vegetable mould on the surface of the earth, we have a demonstrative
proof of the continued destruction of the rocks. {266}
_Ancient encampments and tumuli_. E. de Beaumont adduces the present
state of many ancient encampments and tumuli and of old ploughed fields,
as evidence that the surface of the land undergoes hardly any
degradation. But it does not appear that he ever examined the thickness
of the mould over different parts of such old remains. He relies chiefly
on indirect, but apparently trustworthy, evidence that the slopes of the
old embankments are the same as they originally were; and it is obvious
124