144 AMOUNT OF EAETH Chap. III. 



these gradually increased in numbers as the 

 pasture improved. In the year 1871 a 

 trench was dug on the above slope, and the 

 blades of grass were cut off close to the roots, 

 80 that the thickness of the turf and of the 

 vegetable mould could be measured accur- 

 ately. The turf was rather less than half an 

 inch, and the mould, which did not contain 

 any stones, 2^ inches in thickness. Beneath 

 this lay coarse clayey earth full of flints, like 

 that in any of the neighbouring ploughed 

 fields. This coarse earth easily fell apart 

 from the overlying mould when a spit was 

 lifted up. The average rate of accumulation 

 of the mould during the whole thirty years 

 was only "083 inch per year (i.e., nearly one 

 inch in twelve years) ; but the rate must 

 have been much slower at first, and after- 

 wards considerably quicker. 



The transformation in the appearance of 

 this field, which had been effected beneath 

 my eyes, was afterwards rendered the more 

 striking, when I examined in Knole Park 

 a dense forest of lofty beech-trees, beneath 

 which nothing grew. Here the ground was 

 thickly strewed with large naked stones, and 



