Notices of Memoirs — West Riding Geological Society. 285 



coarser part of tlie deposit, whicli presents the appearance of having 

 been successively dropped down on a sea-bottom. Above and 

 around the more stony accumulations, we often find a considerable 

 thickness of rudely-stratified clay, with few or no stones, which may 

 have been assorted by the ordinary action of the sea. The idea that 

 the " blue clay " was deposited after the extreme rigour of the 

 glacial climate had passed away, accords with the opinion of Mr. 

 Searles V. Wood, Jun,, that the drifts of the North-west of England 

 are newer than those of the South-east. A rather shallow sea, as 

 the land was gradually sinking, and a sea acting principally between 

 about 300 and 600 feet above the present sea-level, would appear to 

 have been the main cause of the distribution of the "blue clay." 

 This sea could not have been much indebted to land-ice sliding 

 down the hill-sides or along the valleys, for such ice would have 

 brought down a supply of materials different from those composing 

 the " blue clay." For the underlying rock and the rock forming the 

 slopes and summits of the hills above it, for great distances, is often 

 Millstone-grit. We are therefore driven to the conclusion that the 

 ice which undoubtedly had a share in shaping the stones and 

 boulders found in the " blue clay" was sea-ice, coast-ice, or ground- 

 ice. Patches of a dark clay, probably of the same age, with a 

 greater or less per centage of limestone boulders, may be found in 

 the Wharfe valley; near Eipon ; around Leeds; filling up abrupt 

 hollows between Wakefield and Doncaster, in a railway cutting near 

 Royston, &c. 



The YelloioisJi-hrown and Variegated Clay. — It is not difficult to 

 understand that after the land had subsided beneath the level which 

 cut off the low-lying source of supply of the "blue clay," the shales 

 and sandstones of the upper Yoredale and Millstone-grit formations 

 composing the sides of the valleys and table-lands, would furnish 

 materials for the " yellowish-brown clay " with its boulders. This 

 clay extends from the bottom of the valleys up to the highest sum- 

 mits of the moors. It contains very little limestone, generally 

 speaking; and that little, from the positions in which it is found, 

 would appear to have been floated by ice. Nine-tenths of the 

 " yellow clay " formation is local, and must have been principally 

 washed out of the hill-sides where it is found. At the bottoms of 

 the valleys, as at Bingley, it graduates into well rounded boulder- 

 gravel. During the accumulation of this Drift, the table-lands and 

 moors must have been completely submerged. 



Stratified Sand and Washed Gravel. — The " blue clay " would ap- 

 pear to have undergone a certain amount of denudation before the 

 "yellow clay" was thrown down above it, as its surface is generally 

 uneven, and apparently eroded. The yellow clay presents indica- 

 tions of its having been denuded before the deposition of the sand 

 and gravel. A part of the sand may have been derived from the 

 "yellow clay," which is often more or less arenaceous, and apart 

 from the direct denudation of the local Carboniferous grits and 

 sandstones. The sand seldom rises higher than about 350 or 400 

 feet above the present level of the sea. In the Aire valley, it is 



VOL. VII. — NO. LXXII. 01 



