CHAP. in. UNDERMINED BY WORMS. 155 



thirty-five years, as far as I could judge, 

 about H inch ; and this must have been due 

 to the brick-rubbish beneath the more pro- 

 tuberant parts having been undermined by 

 worms. At this rate the upper surface of the 

 stone, if it had been left undisturbed, would 

 have sunk to the general level of the field 

 in 247 years; but before this could have 

 occurred, some earth would have been washed 

 down by heavy rain from the castings on the 

 raised border of turf over the upper surface 

 of the stone. 



The second stone was larger than the one 

 just described, viz., 67 inches in length, 39 in 

 breadth, and 15 in thickness. The lower 

 surface was nearly flat, so that the worms 

 must soon have been compelled to eject their 

 castings beyond its circumference. The stone 

 as a whole had sunk about 2 inches into the 

 ground. At this rate it won Id have required 

 262 years for its upper surface to have sunk 

 to the general level of the field. The up- 

 wardly sloping, turf-covered border round 

 the stone was broader than in the last case, 

 viz., from 14 to 16 inches; and why this 

 should be so, I could see no reason. In most 

 parts this border was not so high as in the 



