38 ETON NATURE-STUDY 



for their preference for old gravel walks and paths across fields is still 

 to be discovered. 



If, as Darwin suggested, compression of the soil is favourable to 

 worms, nothing is easier than to imitate these conditions in a large 

 box of earth, in which a known number of worms have been placed. 

 A certain part should then be compressed, and it would be easy to 

 find out whether, after a few days, this contained more worms than 

 the rest of the box. 



It is, however, as natural ploughs and cultivators of the soil that 

 earthworms have excited so much attention. Their finely divided 

 castings, familiar objects to everybody, are, by the action of wind and 

 rain, blown and washed from the surface ; and it has been shown that 

 a layer of earth, *2 of an inch in thickness, is every year brought up 

 by earthworms, resulting, in many places, in a removal of over ten 

 tons of soil per acre. This, in the course of ages, will amount to a 

 vast deal, and is another instance of the important fact already 

 alluded to in Part I, page 125, that the great changes which have 

 taken place and are now taking place on our globe have been and are 

 the result, not of sudden catastrophes but of small agencies continually 

 at work. To quote from Darwin : " When we behold a wide turf- 

 covered expanse, we should remember that its smoothness, on which 

 so much of its beauty depends, is mainly due to all the inequalities 

 having been slowly levelled by worms. The plough is one of the 

 most ancient and most valuable of man's inventions ; but long before 

 he existed, the land was in fact regularly ploughed, as it still con- 

 tinues to be ploughed, by earthworms. It may be doubted whether 

 there are many other animals which have played so important 

 a part in the history of the world as have these lowly organised 

 creatures." * 



* Vegetable Mould and Earthworms, page 313. 



