226 
the ancient aqueduct, known as the Hamhleton Dyke — the 
water of this contains 182 grains per gallon of mineral mat- 
ter, mostly Sulphate of Lime. The shells are all of existing 
kinds, most of which are found still living in the adjoining 
ditches and hedge-banks. The species which I noticed at 
Askern, were Limnoea stagnalis^ L. palustris, and L. peregra, 
Planorbis corneus and P. marginatus, Helix nemoralis and 
Bithinia tentaculata. At Monk Fryston I found Helix caper- 
ata, H. rufescens, H. nemoralis, H. rotundata and H. pulchella, 
Zua lubrica, Limnsea peregra, L. truncatula and L. palustris, 
Bithinia tentaculata, Planorbis marginatus and Yalvata 
piscinalis and a Pisidium. 
6. Warp, — This is the name locally given to a peculiar 
sediment held in suspension in the tidal waters of the Hum- 
ber and its tributaries. It is of a light chocolate colour, 
containing shining flakes of mica, and of a peculiar soft 
silky feel by which it may readily be recognised. The 
appended analysis (Table 1) by my friend Mr. Hunter, 
F.C.S., of Goole, shows that three parts out of four of 
it consist of sand, mica, and other matters insoluble in acid ; 
lime and magnesia together constitute about 6 per cent., and 
alumina an equal proportion. The appearance and physical 
characters of the TVarp are very different from those of the 
sediments deposited by the rivers in the non-tidal portion of 
their course, that of the Ouse being a coarse brown sandy 
loam; of the Aire, a black, loose, woolly-looking earth. The 
Warp too is most abundant at high- water, at spring tides, 
and in dry weather ; and least so at low- water, during neap 
tides, and when much fresh water is coming down the rivers. 
These facts seem to show that it has a different origin from 
the ordinary detritus carried down by rivers, and that origin 
seems to be the materials removed from the rapidly perishing 
coast of Holderness. If so, it consists of the disintegrated 
materials of the boulder clay. It appears to reach its maxi- 
