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find that tlie land adjoining the river is the highest part of 
the district. This bed of Warp is at Goole six feet in thick- 
ness, and is often clayey or sandy at the base. It contains 
no fossils. For the last century or so the practice of 
artificial warping has been carried on. To efiect this, 
large drains have been cut from the river; the land in- 
tended to be warped is enclosed with a high bank, and a 
communication is then made with the warping drain, 
which allows the water to flow over the land at every 
tide. Sometimes in summer-time the doughs at the 
mouth of the drain are closed at spring tide, so as to hold 
up the water and allow it more efiectually to deposit 
its sediment. This process is continued two or three years, 
at the expiration of which time a deposit of sometimes three 
or four feet of rich soil will have accumulated. The pressure 
of this bed of soil compresses the subjacent peat, so that where 
the latter is thick the surface subsides to such an extent that 
another warping may be required in the course of a few years, 
otherwise it is not repeated. 
The physical characters of this district must have 
been greatly changed by the embanking of the rivers, 
which is said to have been done in the reign of Edward 
III. (1327-77), and again by Vermuyden's drainage of 
Hatfield Chase, in the 17th century ; this engineer having 
cut a new channel for the Eiver Don, from Newbridge to 
Groole, and closed that which ran past Crowle into the Humber 
at Adlingfleet. The other mouth, which opened into the Aire 
at Snaith, has been silted up almost within the memory of 
men now living. These old river channels can now hardly be 
traced, except by the local names, and by the course of roads 
and position of buildings. In several places, as at Wistow, 
Selby, and Hemingbrough, the course of the Ouse has altered 
greatly in historic times by cutting through the isthmus 
between two bends, and the silting up of the old channel. 
