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mum in the lower reaches of the Ouse, probably because the 
opposing tendencies of the tide to wash it up, and of the 
river current to carry it down, are there most counter- 
balanced (See Table 2). On the hypothesis that the 
Warp is brought up by the tide from below, the fact that 
it occurs higher up the rivers than the salt water reaches, 
* may be explained by supposing it to be washed up, bit by bit, 
at consecutive tides, the part deposited at one tide being 
carried up a little higher and again deposited at the next. 
The velocity of the flow of the tide being much greater 
than that of the ebb, its carrying power would be pro- 
portionately larger. On the other hand, the sea- salt being 
in solution, would be completely washed away by the water 
coming down from above. 
In water that is at rest, or comparatively still, the Warp 
is soon deposited, and the sand and clay subsiding at 
different rates, the deposit is in distinct laminas, often so thin 
as to resemble the leaves of a book. Hence the sloping sides 
of the river channel are covered with a deposit of firm mud 
in strongly-marked sloping layers ; and as these mud-banks 
are readily removed and re-deposited by a change in the force 
or direction of the current, instructive examples of de- 
nudation on the small scale, and of cross-bedding, may often 
be seen. Of course, when the river overflows the land, the 
Warp held in suspension in the comparatively stagnant water 
is soon deposited. In the Goole district much of the surface 
lies below high- water mark, so that until the river was em- 
banked it would be submerged at every tide, or at any rate 
every spring tide, consequently over a great part of this 
district the peat is covered with a layer of Warp, either 
natural or artificial. The land nearest the river would 
naturally get a greater share of warp than that at a distance, 
as the water which reached the latter would have been 
already partially purified by subsidence, consequently we 
