118 



The Naturalist. 



viz., siliceous, calcareous, clayey, and peaty ; on the warp lands the 

 vegetation partakes of the character both of limestone, of sandy, and 

 of clayey soils. 



The source whence the warp is derived has been a subject of debate, 

 some maintaining that it comes down from above, others that it 

 is washed up from below ; both views are probably partially right. 

 All rivers carry down with them, especially in seasons of flood, a 

 quantity of sand and mud, the detritus from the surface of their 

 gathering grounds, which is deposited in the level part of their course 

 near the sea, forming the mudbanks and shoals met with about the 

 mouths of all their estuaries ; and this at first sight seems the most 

 plausible explanation of the warp. There are, however, difficulties in 

 the way of accepting it; thus, the comparatively scanty sediment found 

 in the rivers above the last locks has different physical characters to 

 the warp found in the tidal portion of their course. Again, as we 

 proceed upwards from Goole we find the warp gradually diminish ; 

 in the tidal portion of the Wharfe there is hardly any. The last fact 

 may perhaps be explained by the circumstance that the tide near its 

 upper limit flows during a very small portion of the day ; the current 

 running towards the sea during the remainder would tend to carry 

 the sediment downwards into the lower reaches. On the other hand 

 there are facts which show that, as far as Goole is concerned, the 

 warp comes from below rather than from above ; thus it is most 

 abundant, like the salt, in dry weather and at spring tides, and least 

 so during floods, at neap tide, and at low water ; and, as I have before 

 said, it diminishes as we proceed upward. Supposing it to come from 

 beloWj there is an obvious source whence it may be derived, viz., the 

 abrasion of the coast of Holderness — a coast which is being worn 

 away by the sea so rapidly that a belt of land averaging a mile in 

 width has been removed since the Norman conquest. Against this 

 view it may be said that the warp reaches higher up the river than 

 the salt does, but the warp being merely held in suspension, may be 

 washed up a bit at a time by consecutive tides, the part deposited 

 being carried a little higher and again partly deposited, and so on, 

 while the salt being in solution would be washed out of it. The mica 

 in the warp may be derived either from the micaceous sandstones of 

 the carboniferous series, supposing it to come down from above, or 

 from the granite boulders of the glacial clays of Holderness. The 

 warp (represented in the table by solids in suspension) appears by my 

 analysis to reach its maximum at Swinefleet, and to diminish thence 



