228 FORMATION AND GROWTH OF 



consequently, if the mould was solely due to them, 

 there would be between it and the subsoil a layer of 

 coarse sand or gravel, formed from the large particles 

 they could not swallow. Even from Darwin's ex- 

 amples it would appear evident that the growth of 

 soil cannot be due to worms alone ; for spread a 

 layer of lime on a field, and the worm, to quote that 

 author, f; is unable to swallow coarse particles, and 

 the finer earth lying beneath would be removed by a 

 slow process to the surface." Thus, eventually, all 

 the matter that could be reduced small enough to be 

 swallowed by the worms would be brought above the 

 lime, and only the pebbles and fragments of stones 

 left below ; so that above there ought to be only this 

 fine earth, while below there ought to be only gravel 

 and sand. This is the result that ought to occur if to 

 the worms alone is due the vegetable soil ; but if they 

 worked in conjunction with the decay of the vege- 

 tables, and principally in the soil due to that decay, 

 there would be a continual shifting of a soil in which 

 few pebbles ever existed. This, however, would involve 

 the surface of the subsoil remaining permanent. 



Nearly all the examples put forward by Darwin 

 were observed in rich, highly-cultivated ground, 

 where earthworms abound ; therefore the growth of 

 the worm-formed soil must have been more rapid 

 than would ordinarily be the case, and the part 

 added, through the decay of the vegetable matter, 



