156 GKEAT STONES Chap. III. 



last case, viz., from 2 to 1\ inches, but in one 

 place it was as much as 5^. Its average 

 height close to the stone was probably about 

 3 inches, and it thinned out to nothing. If 

 so, a layer of fine earth, 15 inches in breadth 

 and 1^ inch in average thickness, of sufficient 

 length to surround the whole of the much 

 elongated slab, must have been brought up 

 by the worms in chief part from beneath the 

 stone in the course of 35 years. This 

 amount would be amply sufficient to account 

 for its having sunk about 2 inches into the 

 ground ; more especially if we bear in mind 

 that a good deal of the finest earth would 

 have been washed by heavy rain from the 

 castings ejected on the sloping border down 

 to the level of the field. Some fresh castings 

 were seen close to the stone. Nevertheless, 

 on digging a large hole to a depth of 18 

 inches where the stone had lain, only two 

 worms and a few burrows were seen, although 

 the soil was damp and seemed favourable for 

 worms. There were some large colonies of 

 ants beneath the stone, and possibly since 

 their establishment the worms had decreased 

 in number. 



The third stone was only about half as 



