field, which had formerly existed as a separate one, and which it was
believed had been pasture-land for more than a century, trenches were dug
to see how thick the vegetable mould was. By chance the first trench was
made at a spot where at some former period, certainly more than forty
years before, a large hole had been filled up with coarse red clay,
flints, fragments of chalk, and gravel; and here the fine vegetable mould
was only from 41 8 to 43 8 inches in thickness. In another and undisturbed
place, the mould varied much in thickness, namely, from 61 2 to 81 2 inches;
beneath which a few small fragments of brick were found in one place.
From these several cases, it would appear that during the last 29 years
mould has been heaped on the surface at an average annual rate of from
0.2 to 0.22 of an inch. But in this district when a ploughed field is
first laid down in grass, the mould accumulates at a much slower rate.
The rate, also, must become very much slower after a bed of mould,
several inches in thickness, has been formed; for the worms then live
chiefly near the surface, and burrow down to a greater depth so as to
bring up fresh earth from below, only during the winter when the weather
is very cold (at which time worms were found in this field at a depth of
26 inches) and during summer, when the weather is very dry.
A field, which adjoins the one just described, slopes in one part rather
steeply (viz., at from 10 to 15 ); this part was last ploughed in 1841,
was then harrowed and left to become pasture-land. For several years it
was clothed with an extremely scant vegetation, and was so thickly
covered with small and large flints (some of them half as large as a
child s head) that the field was always called by my sons the stony
field. When they ran down the slope the stones clattered together, I
remember doubting whether I should live to see these larger flints
covered with vegetable mould and turf. But the smaller stones
disappeared before many years had elapsed, as did every one of the larger
ones after a time; so that after thirty years (1871) a horse could gallop
over the compact turf from one end of the field to the other, and not
strike a single stone with his shoes. To anyone who remembered the
appearance of the field in 1842, the transformation was wonderful. This
was certainly the work of the worms, for though castings were not
frequent for several years, yet some were thrown up month after month,
and these gradually increased in numbers as the pasture improved. In the
year 1871 a trench was dug on the above slope, and the blades of grass
were cut off close to the roots, so that the thickness of the turf and of
the vegetable mould could be measured accurately. The turf was rather
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