SOIL OR SURFACE-MATTER. 233 



possibly enter; yet over all those different kinds 

 of subsoil the surface-mould increases if the land is 

 laid down in permanent grass. The beginning of the 

 formation of the soil over a subsoil of bog iron-ore 

 cannot be due to anything but chemical action and 

 vegetable decay, as no worm-work could have been 

 done there ; and if in such an instance a surface-soil 

 can be formed without the aid of worms, why should 

 not similar work go on in other places ? In such 

 places the formation of soil would be carried on 

 under most adverse circumstances ; for a bare sur- 

 face of limonite is a very unfavourable place for 

 vegetation, and usually it appears due to the decay 

 of the water lodged on the surface, with perhaps a 

 slight disintegration of the underlying mineral, from 

 which are generated lichens and mosses, and event- 

 ually a peaty soil. It is added to, however, very 

 gradually ; for in dry weather, there being no depth 

 of earth, the vegetation withers away. 



Land that has been tilled to one depth for many 

 years will have a surface to its subsoil like a road; and 

 this is so well known, that to counteract it subsoiling 

 has been introduced. If such land is laid down in grass, 

 and subsequently again broken up, the surface of the 

 subsoil caused by the former tilling will be found in- 

 tact; but the depth of the mould will have increased in 

 proportion to the number of years it has remained under 

 grass. This increase cannot have taken place below, 



