NOTICES OF NEW BOOKS. 497 
having drawn an object close to the mouths of their burrows, how 
best to drag it in, they must acquire some notion of its general 
shape, and thus guide their actions by the result of individual 
experience. 
The enormous amount of earth brought annually to the 
surface by worms is very remarkable. By actual experiment— 
that is, by collecting and weighing the castings—it appears that 
in some cases 83 lbs. of earth are brought up to the surface of 
every square yard during the year—an amount which reaches the 
high total of 18 tons per acre; and 10 tons may be taken as a 
very fair average. The number of worms in an acre of land has 
been estimated at between 50,000 and 60,000, their weight being 
nearly 400 lbs. The numerous experiments of this kind made by 
Mr. Darwin give some very curious and at the same time 
astonishing results. One of these experiments lasted about 
thirty years! It was this:—In 1842 a layer of broken chalk was 
spread over old pasture land for the sake of observing at some 
future time the depth to which it would become buried. In 1871 
a trench was dug across the field, and the line of white masses 
was everywhere seven inches from the surface! 
After such experiments as these, it is not difficult to under- 
stand how boulders, monoliths, and ancient monuments, may in 
course of time become gradually buried by the agency of earth- 
worms, to whom antiquaries may be said to be truly indebted. 
The tesselated pavement of Abinger, in Surrey, was covered 
with at least fourteen inches of worm castings; the remains of 
a Roman villa at Chedworth, in Gloucestershire, were concealed 
under thirty-eight inches of similar soil; and the fine villa 
recently discovered at Brading, in the Isle of Wight, had been 
buried by worms to the depth of from three to four feet, the 
floor having gradually sunk as the earth which the annelids piled 
up was removed by them. In lke manner the Roman towns of 
Silchester, in Hampshire, and Wroxeter, in Shropshire, have 
experienced the kindly attention of the worms; while one of the 
fallen blocks at Stonehenge has sunk considerably below the 
level of the surrounding ground through the same agency. 
It must not, however, be forgotten—and Mr. Darwin is careful 
to remind us of this cause of possible error in his own ealcula- 
tions—that the washing down of soil from the neighbouring 
higher lands and the deposition of dust have together aided 
3s 
