appeared fresh or had been recently ejected. We may therefore assume
that those which were weighed had been ejected within, we will say, forty
days from the time when the field was rolled, that is, twelve days short
of the whole intervening period. I had examined the same part of the
field shortly before it was rolled, and it then abounded with fresh
castings. Worms do not work in dry weather during the summer, or in
winter during severe frosts. If we assume that they work for only half
the year though this is too low an estimate then the worms in this field
would eject during the year, 8.387 pounds per square yard; or 18.12 tons
per acre, assuming the whole surface to be equally productive in
castings.
In the foregoing cases some of the necessary data had to be estimated,
but in the two following cases the results are much more trustworthy. A
lady, on whose accuracy I can implicitly rely, offered to collect during
a year all the castings thrown up on two separate square yards, near
Leith Hill Place, in Surrey. The amount collected was, however, somewhat
less than that originally ejected by the worms; for, as I have repeatedly
observed, a good deal of the finest earth is washed away, whenever
castings are thrown up during or shortly before heavy rain. Small
portions also adhered to the surrounding blades of grass, and it required
too much time to detach every one of them.
On sandy soil, as in the present instance, castings are liable to crumble
after dry weather, and particles were thus often lost. The lady also
occasionally left home for a week or two, and at such times the castings
must have suffered still greater loss from exposure to the weather.
These losses were, however, compensated to some extent by the collections
having been made on one of the squares for four days, and on the other
square for two days more than the year.
A space was selected (October 9th, 1870) for one of the squares on a
broad, grass-covered terrace, which had been mowed and swept during many
years. It faced the south, but was shaded during part of the day by
trees. It had been formed at least a century ago by a great accumulation
of small and large fragments of sandstone, together with some sandy
earth, rammed down level. It is probable that it was at first protected
by being covered with turf. This terrace, judging from the number of
castings on it, was rather unfavourable for the existence of worms, in
comparison with the neighbouring fields and an upper terrace. It was
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