levigated state of the castings Fragments of brick in
the castings over ancient buildings well rounded. The
triturating power of worms not quite insignificant
under a geological point of view.
CHAPTER VI.
THE DENUDATION OF THE LAND _continued_.
Denudation aided by recently ejected castings flowing 237 279
down inclined grass-covered surfaces The amount of
earth which annually flows downwards The effect of
tropical rain on worm castings The finest particles of
earth washed completely away from castings The
disintegration of dried castings into pellets, and
their rolling down inclined surfaces The formation of
little ledges on hill-sides, in part due to the
accumulation of disintegrated castings Castings blown
to leeward over level land An attempt to estimate the
amount thus blown The degradation of ancient
encampments and tumuli The preservation of the crowns
and furrows on land anciently ploughed The formation
and amount of mould over the Chalk formation.
CHAPTER VII.
CONCLUSION.
Summary of the part which worms have played in the 280 288
history of the world Their aid in the disintegration of
rocks In the denudation of the land In the preservation
of ancient remains In the preparation of the soil for
the growth of plants Mental powers of worms Conclusion.
INTRODUCTION.
THE share which worms have taken in the formation of the layer of
vegetable mould, which covers the whole surface of the land in every
moderately humid country, is the subject of the present volume. This
mould is generally of a blackish colour and a few inches in thickness.
In different districts it differs but little in appearance, although it
may rest on various subsoils. The uniform fineness of the particles of
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