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clay was thrown down above it, as its surface is generally 
uneven, and apparently eroded. The yellow clay presents 
indications 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 a part 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, where I have principally exa- 
mined it, it is evidently of the same age as the great sand 
formation of the vale of York, though in the vale of York the 
distinction between the sand and stratified gravel is generally 
better defined. About Keighley, Marley, Shipley, &c., the 
sand irregularly alternates with washed gravel. Both the 
sand and washed gravel contain boulders, as already stated, 
and from the position of these boulders it is evident that 
they must have been dropt in. The action of floating ice, 
therefore, could not have ceased during the deposition of the 
sand. In the vale of York, and likewise in the Aire valley, 
the sand contains perfectly angular boulders, as well as 
boulders more or less rounded. During the deposition of the 
sand there would appear to have been rapid currents in a 
shallow sea. The deflected and eddying action of these 
currents in peculiar situations would be likely to leave an 
undulating surface, varied by abrupt eminences. But the 
undulations left by deposition must have been modified by 
contemporaneous or subsequent denudation, for on a very 
uneven surface of sand (a surface unconformable to its strati- 
fication) an upper houlder-clay has been deposited. It may 
either have been derived from the denudation of the yellow 
boulder-clay, or from a direct denudation of shale and rock ; 
and it is difficult to explain its position above the sand 
without supposing a slight reversion in the movement of the 
land, or a second partial subsidence. 
