64 THE MECHANICAL ANAL YSIS OF SOILS [chap, 



tendency of the soil to run and dry with a caked surface, 

 if much rain falls after a fine tilth has been attained. 

 In the soil but not the subsoil there is a fair proportion 

 of calcium carbonate, of artificial origin, and this con- 

 tributes greatly to the workability of the soil, for it has 

 been found unprofitable to retain some of the fields, 

 in which the calcium carbonate is absent, under 

 arable cultivation. Land of this class is still largely 

 under the plough, and is good wheat, mangold, 

 and bean land, but is too heavy for barley or turnips. 

 An occasional bare fallow is desirable to clean the land 

 and bring it into tilth again ; it also yields very fair 

 permanent pasture. 



Soil No. 7 is situated on the Kimeridge Clay forma- 

 tion in Cambridgeshire ; it is heavy land, difficult to 

 cultivate, and when under the plough requires a bare 

 fallow from time to time to restore the tilth. This 

 represents one of the heaviest soils which respond to 

 arable cultivation, which indeed is only practicable 

 because the soil, though containing so high a proportion 

 of clay, also contains a good deal of coarse sand, which 

 keeps it open and helps to render it friable. 



Soil No. 8 is a heavy, undrained London Clay, which 

 at the present time is almost pure pasture. At one time 

 it would carry in favourable seasons heavy crops of 

 wheat and beans, but the expense of cultivation and 

 the danger of missing a season have rendered it quite 

 unprofitable to farm under the plough. With the 

 return of higher prices and the development of 

 mechanical cultivation, which enables the farmer to 

 handle large tracts of land in the short periods during 

 which the soil is fit to move, this land may come back- 

 again into cultivation. But it requires a considerable 

 expenditure of capital on drainage and liming before 

 much can be made of the soil. It will be noticed that 



