CHAP. III. BROUGHT UP BY WORMS. 151 



surface, is a question which has probably 

 never occurred to them.* 



The Sinking of great Stones through the 

 Action of Worms. When a stone of large 

 size and of irregular shape is left on the 

 surface of the ground, it rests, of course, 

 on the more protuberant parts ; but worms 

 soon fill up with their castings all the hollow 

 spaces on the lower side ; for, as Hensen re- 

 marks, they like the shelter of stones. As 

 soon as the hollows are filled up, the worms 

 eject the earth which they have swallowed 

 beyond the circumference of the stones ; 

 and thus the surface of the ground is raised 

 all round the stone. As the burrows ex- 

 cavated directly beneath the stone after a 

 time collapse, the stone sinks a little, t Hence 



* Mr. Lindsay Carnagie, in a letter (June 1838) to Sir C. Lyell, 

 remarks that Scotch farmers are afraid of putting lime on 

 ploughed land until just before it is laid down for pasture, from 

 a belief that it has some tendency to sink. He adds : " Some 

 years since, in autumn, I laid lime on an oat-stubble and ploughed 

 it down ; thus bringing it into immediate contact with the dead 

 vegetable matter, and securing its thorough mixture through the 

 means of all the subsequent operations of fallow. In consequence 

 of the above prejudice, I was considered to have committed a 

 great fault ; but the result was eminently successful, and the 

 practice was partially followed. By means of Mr. Darwin's 

 observations, I think the prejudice will be removed." 



f This conclusion, which, as we shall immediately see, is fully 



