WOKK OF EARTH-WORMS. 191 



The book upon "The Formation of Vegetable 

 Mould Through the Action of. Worms," must be in- 

 cluded among his geological works, although it contains 

 a great many observations of deep zoological interest. 

 It has been stated already that he wrote a paper on 

 this subject for the Geological Society in 1838. In 

 1877 he studied the mode by which Roman remains 

 gain their protective covering of mould ; again towards 

 the end of 1880 he began systematically to prepare the 

 book, which was published on October 10th of the fol- 

 lowing year. It was extremely successful, 8,500 copies 

 being sold in three years. 



This interesting work affords a good illustration of 

 the tremendous results obtained, even in a moderate 

 time, by an immense number of workers all using their 

 powers in one direction. Each single earth-worm 

 swallows earth in the excavation of its burrow and for 

 the nutriment it contains, the waste material being 

 ejected as " castings " at the surface, and as a lining to 

 the burrow. But although the amount of earth thus 

 swallowed by a single worm is not large, worms are so 

 numerous that "the whole of the superficial mould . . . 

 has passed, and will again pass, every few years through 

 the bodies of worms." The result of this unceasing 

 transport of the deeper mould to the surface is shown 

 to be the burial of stones, either singly or in layers (as 

 in paths), the covering and consequent protection of 

 ancient buildings, and the preparation of soil for 

 plants. In addition to this, the geological denuding 

 agencies are assisted by the manner in which the 



