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 less than half an inch, and the mould, which did not contain any stones, 21/2 inches in thickness.  Beneath this lay coarse, clayey earth full of flints, like that in any of the neighboring ploughed fields.  This coarse earth easily fell apart from the overlying mould when a split was lifted up.  The average rate of accumulation of the mould during the whole thirty years was only .083 inch per year (i.e., nearly one inch in twelve years); but the rate must have been much slower at first, and afterwards considerably quicker.

The transformation in the appearance of this field, which had been effected beneath my eyes, was afterwards rendered the more striking, when I examined in Knole Park a dense forest of lofty beech-trees, beneath which nothing grew.  Here the ground was thickly strewed with large, naked stones, and worm-castings were almost wholly absent.  Obscure lines and irregularities on the surface indicated that the land had been cultivated some centuries ago.  It is probable that a thick wood of young beech-trees sprung up so quickly, that time enough was not allowed for worms to cover up the stone with their castings, before the site became unfitted for their existence.  Anyhow, the contrast between the state of the now miscalled “stony field,” well stocked with worms, and the present state of the ground beneath the old beech-trees in Knole Park, where worms appeared to be absent, was striking.

A narrow path running across part of my lawn was paved in 1843 with small flag-stones, set edgeways; but worms threw up many castings, and weeds grew thickly between them.  During several years the path was weeded and swept; but ultimately the weeds and worms prevailed, and the gardener ceased to sweep, merely moving off the weeds, as often as the lawn was mowed.  The path soon became almost covered up, and after several years no trace of it was left.  On removing, in 1877, the thin overlaying layer of turf, the small flag-stones, all in their proper places, were found covered by an inch of fine mould.