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drift of considerable thickness, sometimes amounting to fifty 
feet, which has been partly denuded since its deposit, allowing 
the limestone to crop out here and there, showing sides more 
or less precipitous. Now it is quite clear that if these valleys 
had been excavated since the glacial period, the gravel would 
only have remained as a capping to the limestone, and not, as 
it does now, have covered the sides of the limestone cliffs, as 
well as their tops. This bed of glacial drift is composed of 
sand and clay with rounded pebbles of Carboniferous limestone 
and the harder sandstones of the coal measures. I have 
found also once or twice pieces of granite and greenstone. 
The stones are of all sizes from two or three feet in diameter 
to the finest sand, and are commonly confusedly mixed 
together ; though the lowest deposits seem always to contain 
the largest portion of Carboniferous limestone. Generally 
these deposits are horizontal ; but, here and there, there are 
patches of sand, several feet in thickness, which occur in 
pockets in the gravel. Where the beds have not been subse- 
quently disturbed the limestone pebbles are all polished and 
covered with fine sharp scratches. Upon the pebbles from 
the other formations I have not been able to discover any 
scratches, though many of them are worn quite smooth ; but 
the texture of the stone is such that it is very unlikely that 
they should have retained any of the scratches which they 
might once have received. 
To the east this bed of drift passes imperceptibly into the 
general superficial deposits of the vale of York, but on the 
west its outline is sharp and definite, scarcely ever extending 
more than half a mile beyond the boundary of the magnesian 
limestone. The drift which lies still further westward is 
perfectly local, derived from the beds immediately below; 
whereas this seems to me to have been brought from the 
upper parts of Wensleydale on the drifting ice of the glacial 
period, and deposited upon the top of the submerged ridge of 
