DAVIS! SOURCE OF BOULDERS IN CALDER VALLEY. 149 
sands frequently exhibit very irregular stratification, and 
occasionally the beds are much contorted, as if from lateral 
pressure, such as might be produced by icebergs grounding 
in shallow water."* 
There is little trace of glacial deposits on the Permian 
limestone, but on the western side, in the valley of the 
Aire, there is abundant evidence of glacial action. The 
hollow in which Bradford is situated is covered with a thick 
deposit of boulder clay, and at Guiseley and Apperley 
Bridge patches of similar drift occur. North of Leeds great 
masses of drift are found, consisting principally of stiff blue 
clay, containing rounded and angular stones of local origin, 
as sandstones and grit, and also many others of foreign 
origin, granite and trap being the most common. At Whin- 
moor, at a height of 380 feet above the sea-level, a boring 
went through 114 feet of boulder clay. These deposits are 
probably the remains of an old glacier which descended 
the valley of the Aire from the neighbourhood of Skipton. 
It is within the range of possibility that this glacier may 
have extended as far south as the neighbourhood of Barns- 
ley, for Prof. A. H. Green has described a bed of glacial 
clayf filling a basin-shaped hollow about two miles north of 
that town. The exposure is three-quarters of a mile in 
length : the boulder clay is divided into upper and lower, 
and contains, besides stones of local origin, boulders of 
highly metamorphosed breccia, granite, and others, from 
the Lake District. There are other patches of glacial clay 
scattered over the district, and also quantities of drift. 
From a consideration of all the facts, Prof. Green arrives at 
the conclusion that the whole district was probably covered 
by a layer of till or boulder clay, resulting from the presence 
* Memoir of the Geological Survey, Illustrating Sheet 93 N. W. p. 14. 
f Proc. York. Geol. and Polyt. Soc, 1876, new series, pt. iii., p. 122. 
