Chap. III. ANNUALLY ACCUMULATED. 173 



again measured. The drying caused it to 

 shrink by ^- of its original bulk, judging from 

 exterior measurements alone. It was then 

 triturated and partly reduced to powder, in the 

 same manner as the castings had been treated, 

 and its bulk now exceeded (notwithstanding 

 shrinkage from drying) by -^ that of the 

 original block of damp mould. Therefore the 

 above calculated thickness of the layer, formed 

 by the castings from the Terrace, after being 

 damped and spread over a square yard, would 

 have to be reduced by -^; and this will 

 reduce the layer to '09 of an inch, so that a 

 layer *9 inch in thickness would be formed in 

 the course of ten years. On the same prin- 

 ciple the castings from the Common would 

 make in the course of a single year a layer 

 *1429 inch, or in the course of 10 years 1*429 

 inch, in thickness. We may say in round 

 numbers that the thickness in the former case 

 would amount to nearly 1 inch, and in the 

 second case to nearly 1J inch in 10 years. 



In order to compare these results with 

 those deduced from the rates at which small 

 objects left on the surfaces of grass-fields 

 become buried (as described in the early part 



