JOWETT AND MUFF I GLACIATION OF BRADFORD, ETC. 215 
sandy, and containing less limestone, as the valley is ascended. 
Above Oxenhope patches of drift occur below a limit on the 
hill side. In Sun Hill Clough thin boulder-clay, with chert 
and limestone, were found up to 1,100 feet. In Holden Clough 
boulder-clay occurs up to 1,050 feet. To the south of Leeming, 
in Isle Lane, sandy boulder-clay, with encrinital limestone 
pebbles, was found between the 1,000 and 1,050- foot contours. 
In Harden Clough and the next one to the east boulder-clay 
occurred at the same height. Above this altitude, and right 
up to the Aire and Calder watershed, we have found no glacial 
deposits, nor even scattered rounded stones, such as are found 
on areas free from boulder-clay and gravel at lower levels. The 
same observation applies to Thornton Moor and the high ground 
to the east as far as the Queensbury ridge. It holds good also 
for the moors to the west and north-west, except that the 
boulder-clay or scattered drift pebbles have been found to 
extend to 1,400 feet in places. The absence of drift deposits, 
and, indeed, of all signs of glaciation on these moors has been 
remarked by previous observers. There are many natural 
hollows in the area where boulder-clay might accumulate and 
be preserved. It seems that we have here an unglaciated area 
which separated the ice-sheet of Lancashire from the Airedale 
glacier. The absence of till from Calderdale, and the occurrence 
of a boulder-clay with far-travelled erratics on the Lancashire 
side of the Pennines, immediately to the west, is in agreement 
with this conclusion. The driftless area described above is 
the extension northwards along the Pennine ridge of a large 
unglaciated district on the eastern slopes of the Pennines, of 
which Calderdale forms a part. On the south side of Airedale 
the upper limit of the drift diminishes in altitude in an easterly 
direction, but not at the same rate as the Aire-Calder watershed. 
The drift surmounts the latter near Bradford, as will be described 
later (p. 218). 
The ridge between the Harden and Worth Valleys is bare 
of drift, but the striae recorded above (p. 209) prove that the 
ridge has been over-ridden by the ice from the north-west. 
As in the case of the Worth there is much drift in the lower 
parts of the Harden Valley. Above Cullingworth and Wilsden 
