256 CAUSES OF FERTILITY AND STERILITY [chap. 



uniform deposit all over the land and to distribute 

 the valuable fine silt which settles furthest from 

 the inlet. In some cases the sluice gates are auto- 

 matic, and water is admitted and drawn off at 

 every tide, but in others only every other tide is 

 admitted, thus giving time for the deposit of the finer 

 particles, and greatly improving the character of the 

 resulting land. As a rule, only the spring tides are 

 utilised, because the suspended matter is then at its 

 maximum, and the process is confined to the summer 

 months, to avoid danger from flooding when there is 

 much land water about. In exceptional cases land 

 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 M warping." 



Marling and Claying. 

 Many light and blowing sands, almost too pure to 



