beneath the top of the sloping turf-covered
border.

[Illustration: FIG. 3.
Section through one of the fallen Druidical stones at Stonehenge,
showing how much it had sunk into the ground.]

Sufficient evidence has now been given showing that small objects left
on the surface of the land where worms abound soon get buried, and
that large stones sink slowly downwards through the same means. Every
step of the process could be followed, from the accidental deposition
of a single casting on a small object lying loose on the surface, to
its being entangled amidst the matted roots of the turf, and lastly to
its being embedded in the mould at various depths beneath the surface.
When the same field was re-examined after the interval of a few years,
such objects were found at a greater depth than before. The
straightness and regularity of the lines formed by the embedded
objects, and their parallelism with the surface of the land, are the
most striking features of the case; for this parallelism shows how
equably the worms must have worked; the result being, partly the
effect of the washing down of the fresh castings by rain. The specific
gravity of the objects does not affect their rate of sinking, as could
be seen by porous cinders, burnt marl, chalk and quartz pebbles,
having all sunk to the same depth within the same time. Considering
the nature of the sub-stratum, which at Leith Hill Place was sandy
soil including many bits of rock, and at Stonehenge, chalk-rubble with
broken flints; considering, also, the presence of the turf-covered
sloping border of mould round the great fragments of stone at both
these places, their sinking does not appear to have been sensibly
aided by their weight, though this was considerable.

_On the number of worms which live within a given space._--We will
now show, first, what a vast number of worms live unseen by us beneath
our feet, and, secondly, the actual weight of the earth which they
bring up to the surface within a given space and within a given time.
Hensen, who has published so full and interesting an account of the
habits of worms, calculates, from the number which he found in a
measured space, that there must exist 133,000 living worms in a
hectare of land, or 53,767 in an acre. This latter number of worms
would weigh 356 pounds, taking Hensen's standard of the weight of a
single worm, namely, one gram. It should, however, be noted that this
calculation is founded on the number