layer .9 inch in thickness would be formed in the course of ten years. On the same principle 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 1½ 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 of this chapter), we will give the following summary:—
The accumulation of mould during 14¾ years on the surface of a dry, sandy, grass-field near Maer Hall, amounted to 2.2 inches in 10 years.
The accumulation during 21½ 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