296 CAUSES OF FERTILITY AND STERILITY [chap. 



may be warped 2 or 3 feet deep in one year from 

 January to June in other cases, where the water is 

 less charged with sediment, or the land is at a higher 

 level, an efficient warping, which should not be less 

 than 18 inches deep, requires three or four years. 

 When finished, the land is allowed to dry and con- 

 solidate, drainage grips are then thrown out, and a 

 light crop of oats, in which are sown clover and rye- 

 grass, is taken ; after the seeds have been down two 

 years the land is generally ready to carry wheat. 

 Warp soils are, as a rule, fertile, and noted for 

 growing seed corn of high quality ; they are to all 

 intents and purposes artificial alluvial soils, composed 

 entirely of the finer sands and silts without much 

 clay material, and are comparatively rich in organic 

 debris and other plant food, except perhaps potash. 

 The fertilising of the Egyptian land by the red Nile 

 flood water, the formation and improvement of river 

 meadows by winter flooding, are both analogous to 

 the process of " warping." 



Marling and Claying. 



Many light and blowing sands, almost too pure to 

 permit of any vegetation, have in their immediate 

 neighbourhood a bed of marl or clay which can be 

 easily incorporated, practically creating a soil where 

 there was none before. Among the New Red Sand- 

 stones of Cheshire and the Midland Counties beds of 

 true marl occur and were at one time enormously 

 worked, so that every farm and almost every field shows 

 its old marl pit ; the sandy Lower Greensand soils in 

 the Woburn district have been extensively marled from 

 the adjoining Oxford clay, and many of the Norfolk 

 soils have been made out of blowing sands, by bringing 

 up the clay which immediately underlies them. The 



