09 of an inch, so that a layer 0.9 inch in thickness
would be formed in the course of ten years. On the same principle
the castings from the Common would make in the course of a single
year a layer 0.1429 inch, or in the course of 10 years 1.429 inch,
in thickness. We may say in round numbers that the thickness in
the former case would amount to nearly 1 inch, and in the second
case to nearly 1.5 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 14.75 years on the surface of a
dry, sandy, grass-field near Maer Hall, amounted to 2.2 inches in
10 years.
The accumulation during 21.5 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.
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