to the slope.
_Castings blown to leeward by the wind_. We have seen that moist castings
flow, and that disintegrated castings roll down any inclined surface; and
we shall now see that castings, recently ejected on level grass-covered
surfaces, are blown during gales of wind accompanied by rain to leeward.
This has been observed by me many times on many fields during several
successive years. After such gales, the castings present a gently
inclined and smooth, or sometimes furrowed, surface to windward, while
they are steeply inclined or precipitous to leeward, so that they
resemble on a miniature scale glacier-ground hillocks of rock. They are
often cavernous on the leeward side, from the upper part having curled
over the lower part. During one unusually heavy south-west gale with
torrents of rain, many castings were wholly blown to leeward, so that the
mouths of the burrows were left naked and exposed on the windward side.
Recent castings naturally flow down an inclined surface, but on a grassy
field, which sloped between 10 and 15 , several were found after a heavy
gale blown up the slope. This likewise occurred on another occasion on a
part of my lawn where the slope was somewhat less. On a third occasion,
the castings on the steep, grass-covered sides of a valley, down which a
gale had blown, were directed obliquely instead of straight down the
slope; and this was obviously due to the combined action of the wind and
gravity. Four castings on my lawn, where the downward inclination was 0
45 , 1 , 3 and 3 30 (mean 2 45 ) towards the north-east, after a
heavy south-west gale with rain, were divided across the mouths of the
burrows and weighed in the manner formerly described. The mean weight of
the earth below the mouths of burrows and to leeward, was to that above
the mouths and on the windward side as 23 4 to 1; whereas we have seen that
with several castings which had flowed down slopes having a mean
inclination of 9 26 , and with three castings where the inclination was
above 12 ; the proportional weight of the earth below to that above the
burrows was as only 2 to 1. These several cases show how efficiently
gales of wind accompanied by rain act in displacing recently ejected
castings. We may therefore conclude that even a moderately strong wind
will produce some slight effect on them.
Dry and indurated castings, after their disintegration into small
fragments or pellets, are sometimes, probably often, blown by a strong
wind to leeward. This was observed on four occasions, but I did not
sufficiently attend to this point. One old casting on a gently sloping
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