118 GEEAT STONES Chap. IlL 



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 

 1 soon as the hollows are filled up, the worms 

 1 eject the earth which they have swallowed 

 Ibeyond the circumference of the stones ; 

 |and thus the surface of the ground is raised 

 g.11 r ound the stone. As the burrows ex- 

 cavated directly beneath the stone after a 

 time collapse, the stone sinks a little.* Hence 

 it is, that boulders which at some ancient 



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 pa/rtially followed. By means of Mr. Darwin's 

 obseivations, I think the prejudice will be removed." 



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

 j ustified, is of some little importance, as the so-called bench-stones, 

 which surveyors fix in the ground as a record of their levels, 

 may in time become false standards. My son Horace intends at 

 some future period to ascertain how far this has occurred. 



