even a long lapse of time. It may, however, be urged that at long
intervals, debacles of rain or water-spouts would remove all the mould
from a very gentle slope; but when examining the steep, turf-covered
slopes in Glen Roy, I was struck with the fact how rarely any such event
could have happened since the Glacial period, as was plain from the
well-preserved state of the three successive roads or lake-margins.
But the difficulty in believing that earth in any appreciable quantity
can be removed from a gently inclined surface, covered with vegetation
and matted with roots, is removed through the agency of worms. For the
many castings which are thrown up during rain, and those thrown up some
little time before heavy rain, flow for a short distance down an inclined
surface. Moreover much of the finest levigated earth is washed
completely away from the castings. During dry weather castings often
disintegrate into small rounded pellets, and these from their weight
often roll down any slope. This is more especially apt to occur when
they are started by the wind, and probably when started by the touch of
an animal, however small. We shall also see that a strong wind blows all
the castings, even on a level field, to leeward, whilst they are soft;
and in like manner the pellets when they are dry. If the wind blows in
nearly the direction of an inclined surface, the flowing down of the
castings is much aided.
The observations on which these several statements are founded must now
be given in some detail. Castings when first ejected are viscid and
soft; during rain, at which time worms apparently prefer to eject them,
they are still softer; so that I have sometimes thought that worms must
swallow much water at such times. However this may be, rain, even when
not very heavy, if long continued, renders recently-ejected castings
semi-fluid; and on level ground they then spread out into thin, circular,
flat discs, exactly as would so much honey or very soft mortar, with all
traces of their vermiform structure lost. This latter fact was sometimes
made evident, when a worm had subsequently bored through a flat circular
disc of this kind, and heaped up a fresh vermiform mass in the centre.
These flat subsided discs have been repeatedly seen by me after heavy
rain, in many places on land of all kinds.
_On the flowing of wet castings_, _and the rolling of dry disintegrated
castings down inclined surfaces_. When castings are ejected on an
inclined surface during or shortly before heavy rain, they cannot fail to
flow a little down the slope. Thus, on some steep slopes in Knole Park,
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