Chap. Yl. AIDED BY WORMS. 265 



of the burrow, which was discovered by slicing 

 off the turf; and all the ejected earth was 

 separately collected, namely the part above 

 the hole and the part below. Afterwards 

 these two parts were weighed. In every 

 case there was much more earth below than 

 above ; the mean weight of that above being 

 103 grains, and of that below 205 grains ; so 

 that the latter was very nearly double the 

 former. As on level ground castings are 

 commonly thrown up almost equally round 

 the mouths of the burrows, this difference in 

 weight indicates the amount of ejected earth 

 which had flowed down the slope. But very 

 many more observations would be requisite 

 to arrive at any general result ; for the 

 nature of the vegetation and otber accidental 

 circumstances', such as the heaviness of the 

 rain, the direction and force of the wind, &c., 

 appear to be more important in determining 

 the quantity of the earth which flows down a 

 slope than its angle. Thus with four castings 

 on my lawn (included in the above eleven) 

 where the mean slope was 7° 19', the difference 

 in the amount of earth above and below the 

 burrows was greater than with three other 



