Moreover some of the finest earth of which they were composed must have
been washed completely away to a still greater distance. In drier sites
near Calcutta, a species of worm ejects its castings, not in vermiform
masses, but in little pellets of varying sizes: these are very numerous
in some places, and Mr. Scott says that they are washed away by every
shower.
I was led to believe that a considerable quantity of fine earth is washed
quite away from castings during rain, from the surfaces of old ones being
often studded with coarse particles. Accordingly a little fine
precipitated chalk, moistened with saliva or gum-water, so as to be
slightly viscid and of the same consistence as a fresh casting, was
placed on the summits of several castings and gently mixed with them.
These castings were then watered through a very fine rose, the drops from
which were closer together than those of rain, but not nearly so large as
those in a thunderstorm; nor did they strike the ground with nearly so
much force as drops during heavy rain. A casting thus treated subsided
with surprising slowness, owing as I suppose to its viscidity. It did
not flow bodily down the grass-covered surface of the lawn, which was
here inclined at an angle of 16 20 ; nevertheless many particles of the
chalk were found three inches below the casting. The experiment was
repeated on three other castings on different parts of the lawn, which
sloped at 2 30 , 3 and 6 ; and particles of chalk could be seen between
4 and 5 inches below the casting; and after the surface had become dry,
particles were found in two cases at a distance of 5 and 6 inches.
Several other castings with precipitated chalk placed on their summits
were left to the natural action of the rain. In one case, after rain
which was not heavy, the casting was longitudinally streaked with white.
In two other cases the surface of the ground was rendered somewhat white
for a distance of one inch from the casting; and some soil collected at a
distance of 21 2 inches, where the slope was 7 , effervesced slightly when
placed in acid. After one or two weeks, the chalk was wholly or almost
wholly washed away from all the castings on which it had been placed, and
these had recovered their natural colour.
It may be here remarked that after very heavy rain shallow pools may be
seen on level or nearly level fields, where the soil is not very porous,
and the water in them is often slightly muddy; when such little pools
have dried, the leaves and blades of grass at their bottoms are generally
coated with a thin layer of mud. This mud I believe is derived in large
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