90 AGRICULTURE 



country, notably Warwickshire, almost every 

 field contains a large depression from which 

 marl must have been drawn in great quan- 

 tities a hundred years or more ago. Marl 

 is essentially clay containing ten per cent, or 

 more of carbonate of lime, and that it is 

 capable of improving soil is evident from 

 the fact that enormous quantities were used 

 in the past, before more concentrated fer- 

 tilizing agents were placed within reach of 

 farmers. 



A form of amelioration that is much in 

 evidence along the tidal reaches of the Ouse, 

 the Trent, and the Humber, is Warping 

 This can only be practised on low-lying, level 

 land, situated close to a sluggish tidal river. 

 In the estuary large quantities of mud are 

 deposited, and, when the tide rises, this mud 

 is violently churned up, and more so under 

 certain conditions of the river and tide than 

 others. The adjoining land is provided with 

 embankments supplied with suitable sluices, 

 and when the mud-laden tide rises a portion 

 of the water is allowed to flow over the area 

 thus surrounded, where it is retained until 

 most of the mud and silt has been deposited. 

 This having been effected, the water is 

 allowed to escape, when it will be found that 

 a muddy covering, an inch more or less in 



