e this could have occurred, some
earth would have been washed down by heavy rain from the castings on
the raised border of turf over the upper surface of the stone.

[Illustration: FIG. 2.
Transverse section across a large stone, which had lain on a
grass-field for thirty-five years. _aa_, general level of the
field. The underlying brick of rubbish has not been represented.]

The second stone was larger than the one just described, viz.,
67 inches in length, 39 in breadth, and 15 in thickness. The lower
surface was nearly flat, so that the worms must soon have been
compelled to eject their castings beyond its circumference. The stone
as a whole had sunk about 2 inches into the ground. At this rate it
would have required 262 years for its upper surface to have sunk to
the general level of the field. The upwardly sloping, turf-covered
border round the stone was broader than in the last case, viz., from
14 to 16 inches; and why this should be so, I could see no reason. In
most parts this border was not so high as in the last case, viz., from
2 to 21/2 inches, but in one place it was as much as 51/2. Its average
height close to the stone was probably about 3 inches, and it thinned
out to nothing. If so, a layer of fine earth, 15 inches in breadth and
11/2 inch in average thickness, of sufficient length to surround the
whole of the much elongated slab, must have been brought up by the
worms in chief part from beneath the stone in the course of 35 years.
This amount would be amply sufficient to account for its having sunk
about 2 inches into the ground; more especially if we bear in mind
that a good deal of the finest earth would have been washed by heavy
rain from the castings ejected on the sloping border down to the level
of the field. Some fresh castings were seen close to the stone.
Nevertheless, on digging a large hole to a depth of 18 inches where
the stone had lain, only two worms and a few burrows were seen,
although the soil was damp and seemed favorable for worms. There were
some large colonies of ants beneath the stone, and possibly since
their establishment the worms had decreased in number.

The third stone was only about half as large as the others; and two
strong boys could together have rolled it over. I have no doubt that
it had been rolled over at a moderately recent time, for it now lay at
some distance from the two other stones at the bottom of a little
adjoining slope. It rested also on fine e