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 inches 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 larvæ 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 county these latter several agencies appear to be of quite subordinate importance in comparison. with the action of worms.

We have no means of judging how great a weight of earth a single full-sized worm ejects during a year. Hensen estimates that 53,767 worms exist in an acre of land; but this is founded on the number found in gardens, and he believes that only about half as many live in corn-fields. How many live in old pasture land is unknown; but if we assume that half the above number, or 26,886 worms live on such land, then taking from the previous summary 15 tons as the weight of the castings annually thrown up on an acre of land, each worm must annually eject 20 ounces. A fullsized casting at the mouth of a single burrow often exceeds, as we have seen, an ounce in weight; and it is probable that worms eject more than 20 full-sized castings during a year. If they eject annually more than 20 ounces, we may infer that the worms which live in an acre of pasture land must be less than 26,886 in number.

Worms live chiefly in the superficial mould,

which is usually from 4 or 5 to 10 and even 12 inches in thickness; and it is this mould which passes over and over again through their bodies and is brought to the surface. But worms occasionally burrow into the subsoil to a much greater depth, and on such occasions they bring up earth from this greater depth; and this process has gone on for countless ages. Therefore the superficial layer of mould would ultimately attain, though at a slower and slower rate, a thickness equal to the depth to which worms ever burrow, were there not other opposing agencies at work which carry away to a lower level some of the finest earth which is continually being brought to the surface by worms. How great a thickness vegetable mould ever attains, I have not had good opportunities for observing; but in the next chapter, when we consider the burial of ancient buildings, some facts will be given on this head. In the two last chapters we shall see that the soil is actually increased, though only to a small degree, through the agency of worms; but their chief work is to sift the finer from the coarser particles, to

mingle the whole with vegetable débris, and to saturate it with their intestinal secretions.

Finally, no one who considers the facts given in this chapter-on the burying of small objects and on the sinking of great stones left on the surface on the vast number of worms which live within a moderate extent of ground-on the weight of the castings ejected from the mouth of the same burrow-on the weight of all the castings ejected within a known time on a measured space-will hereafter, as I believe, doubt that worms play an important part in nature.

CHAPTER IV.

THE PART WHICH WORMS HAVE PLAYED IN

THE BURIAL OF ANCIENT BUILDINGS.

The accumulation of rubbish on the sites of great cities independent of the action of worms-The burial of a Roman villa at Abinger-The floors and walls penetrated by wormsSubsidence of a modern pavement-The buried pavement at Beaulieu Abbey-Roman villas at Chedworth and Brading— The remains of the Roman town at Silchester-The nature of the débris by which the remains are covered-The penetration of the tesselated floors and walls by worms-Subsidence of the floors-Thickness of the mould-The old Roman city of Wroxeter-Thickness of the mould-Depth of the foundations of some of the Buildings-Conclusion.

ARCHEOLOGISTS are probably not aware how much they owe to worms for the preservation of many ancient objects. Coins, gold ornaments, stone implements, &c., if dropped on the surface of the ground, will infallibly be buried by the castings of worms in a few years, and will thus be safely preserved, until the land at some future time is turned up For instance, many years ago a grass-field