174 THICKNESS OF THE MOULD Chap. III. 



of this chapter), we will give the following 

 summary : — 



Summary of the thickness of the Mould accumulated 

 over Objects left strewed on the Surface, in the 

 course 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 during 30 years on the side of a valley over 

 the Chalk at Down, the soil being argillaceous, very poor, and 

 only just converted into pasture (so that it was for some years 

 unfavourable for worms), amounted to 0*83 inches in 10 years. 



In these cases (excepting the last) it may- 

 be seen that the amount of earth brought 

 to the surface during 10 years is somewhat 

 greater than that calculated from the castings 

 which were actually weighed. This excess 

 may be partly accounted for by the loss which 

 the weighed castings had previously under- 

 gone through being washed by rain, by the 

 adhesion of particles to the blades of the sur- 

 rounding grass, and by their crumbling when 

 dry. Nor must we overlook other agencies 



