Chap. III. ANNUALLY ACCUMULATED, 171 



layer "9 inch in thickness would be formed in 

 the coui'se 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 IJ 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 bui;ied (as described in the early part 

 of this chapter), we will give the following 

 summary : — 



SUMMAEY OF THE THICKNESS OF THE MoULD ACCUMULATED 



ovBB Objects left stbewed on the Subface, in the 



COUKSE OF ten YEARS. 



The accumulation of mould during 14f years on the surface 

 of a dry, sandy, grass-field near Maer Hall, amounted to 2 "2 

 inches in 10 years. 



The accumulation during 21^ years on a swampy field near 

 Maer Hall, amounted to nearly 1 ■ 9 inch in 10 years. 



The accumulation during 7 years on a very swampy field near 

 Maer Hall amounted to 2 • 1 inches in 10 years. 



The accumulation during 29 years, on good, argillaceous 

 pasture-land over the Chalk at Down, amounted to 2 • 2 inches in 

 10 years. 



The accumulation durmg 30 years on the side of a valley over 



