Bibliographical Notice. 445 
to pressure or to atmospheric agencies, facilitate small movements 
of the soil, changing the position of its component particles. The 
author says, ‘* The plough is one of the most ancient and most valu- 
able of man’s inventions; but long before he existed the land was 
in fact regularly ploughed, and still continues to be ploughed, by 
earth-worms.” 
But the most striking action of worms in working the soil con- 
sists in the transport of great quantities of mould to the surface, 
where it can be exposed to the action of the air, spread over the 
surface by rains, and thus serve as new nourishment for growing 
plants. This is effected by the worms coming to the mouths of their 
burrows with their intestines full of mould, which is then discharged 
upon the surface in the well-known conyoluted bodies known as 
worm-casts or castings. It was to this characteristic of the action 
of worms that Mr. Darwin’s first observations related; and he 
showed by the gradual and uniform sinking of top-dressings of 
various kinds (lime, cinders, burnt marl, &c.) that it was a real 
factor in nature. Substances unfit for the food of worms, and too 
large for them to swallow, if lying on the surface of the soil are 
slowly but continuously involved in a layer of soil brought up from 
below them and discharged at the surface, while at the same time 
and by the same process they are to an equal extent undermined. 
The phenomenon, in fact, consists of a transfer of the substance of 
the more deeply-seated layers of mould to the surface; and as such 
objects as bones, stones, &c. must remain in contact with the sur- 
face on which they were originally deposited, they are compelled to 
sink with it beneath the fresh layers of earth brought up. ‘To show 
the important effects thus produced upon the general face of the 
land, we may cite an example adduced by Mr. Darwin from his 
experience in one of his fields at Down. He says that a sloping 
part of this field ‘‘ was last ploughed in 1841, was then harrowed, 
and left to become pasture-land. For several years it was clothed 
with an extremely scant vegetation, and was so thickly covered 
with small and large flints (some of them half as large as a child’s 
head) that the field was always called by my sons ‘ the stony field.’ 
When they ran down the slope the stones clattered together. I 
remember doubting whether I should live to see these larger flints 
covered with vegetable mould and turf. But the smaller stones 
disappeared before many years had elapsed, as did every one of the 
larger ones after a time; so that after thirty years (1871) a horse 
could gallop over the compact turf from one end of the field to the 
other and not strike a single stone with his shoes. . . . This was 
certainly the work of the worms ; for, though castings were not fre- 
quent for several years, yet some were thrown up month after month, 
and these gradually increased in numbers as the pasture improved.” 
A trench cut in 1871 showed a thickness of 3 an inch of turf and 
24 inches of vegetable mould, beneath which lay clayey earth full 
of flints like that in the neighbouring ploughed fields. The rate of 
formation of the mould in this case is certainly very slow, not more 
on the average than an inch in twelve years; but, slow as it is, it 
