SOIL AND SURFACE CONDITIONS 131 



artificial drainage, until the line is reached at which 

 higher temperatures, and a reduced rainfall bring about 

 the decomposition of raw humus at the normal rate. Peat 

 is never formed on porous soils at low eleyations, except 

 in the extreme west of Ireland or Scotland, The low-lying 

 peat bogs of the ordinary kind found in Ireland, Scotland, 

 and many parts of England are due to stagnation of soil 

 water, and the removal of alkaline salts, but have nothing 

 to do with the climate. Mountain peat, on the other 

 hand, is a definite climatic product, as it invariably ceases 

 in that form at altitudes below 1000 or 1500 feet, or prac- 

 tically at the limit of tree growth, apart from the stunted 

 form of the latter capable of growing on peat itself 



For economic purposes the surface soils of the country 

 may be roughly divided into three classes — first, soils 

 formed on the more recent beds and drift-covered sur- 

 faces consisting of sand, gravel, clay, or loam of consider- 

 able depth; second, rocky surfaces generally bare of 

 ordinary soil, but broken up by crevices, and pockets 

 of soil or gravel, with which may be classed thin soils 

 produced by the weathering of the softer rocks ; third, 

 surfaces covered with peat of various depths; fourth, 

 practically bare rock, or surfaces carrying a soil not more 

 than a few inches in depth, on an impervious subsoil. 



Loamy clays and sandy loams are usually adapted for 

 tillage or pasture, and are generally found under intensive 

 agriculture, and no possibility at present exists of their 

 becoming available for forestry purposes. Many of them 

 carry a great deal of old woodland, game cover, and 

 plantations adjoining parks and demesnes, and, managed 

 on economic lines, they should produce a high return in 

 timber. In the south of England they are often covered 

 with coppice, which is incapable, under present market 

 conditions, of giving much profit. 



What proportions of the drift soils in the British Isles 



