nearly 11 2 inch in 10 years.
In order to compare these results with those deduced from the rates at
which small objects left on the surfaces of grass-fields become buried
(as described in the early part of this chapter), we will give the
following summary:
SUMMARY OF THE THICKNESS OF THE MOULD ACCUMULATED OVER OBJECTS LEFT
STREWED ON THE SURFACE, IN THE COURSE OF TEN YEARS.
The accumulation of mould during 143 4 years on the surface of a dry,
sandy, grass-field near Maer Hall, amounted to 2.2 inches in 10 years.
The accumulation during 211 2 years on a swampy field near Maer Hall,
amounted to nearly 1.9 inch in 10 years.
The accumulation during 7 years on a very swampy field near Maer Hall
amounted to 2.1 inches in 10 years.
The accumulation during 29 years, on good, argillaceous pasture-land
over the Chalk at Down, amounted to 2.2 inches in 10 years.
The accumulation during 30 years on the side of a valley over the
Chalk at Down, the soil being argillaceous, very poor, and only just
converted into pasture (so that it was for some years unfavourable for
worms), amounted to 0.83 inch in 10 years.
In these cases (excepting the last) it may be seen that the amount of
earth brought to the surface during 10 years is somewhat greater than
that calculated from the castings which were actually weighed. This
excess may be partly accounted for by the loss which the weighed castings
had previously undergone through being washed by rain, by the adhesion of
particles to the blades of the surrounding grass, and by their crumbling
when dry. Nor must we overlook other agencies which in all ordinary
cases add to the amount of mould, and which would not be included in the
castings that were collected, namely, the fine earth brought up to the
surface by burrowing larv and insects, especially by ants. The earth
brought up by moles generally has a somewhat different appearance from
vegetable mould; but after a time would not be distinguishable from it.
In dry countries, moreover, the wind plays an important part in carrying
dust from one place to another, and even in England it must add to the
mould on fields near great roads. But in our country these latter
several agencies appear to be of quite subordinate importance in
comparison with the action of worms.
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