318 J. W. Davis — Erratic Boulders of the Colder Valley. 



granite, trap, syenite, and others, derived from the mountainous dis- 

 tricts, are common, and mixed with these there are also boulders of 

 sandstone, chert, and chalk. The centre of the valley is covered with 

 deposits of a more recent origin ; sands and gravel occur plentifully, 

 and appear to have been derived from the glacial clays beneath by 

 the disintegrating action of water. The stones are generally more 

 rounded, and the strias or ice-scratches have been removed by attri- 

 tion. In a few cases, the boulders still retain scratches. " These 

 sands frequently exhibit very irregular stratification, and occasion- 

 ally the beds are much contorted, as if from lateral pressure, such as 

 might be produced by icebergs grounding in shallow water." x 



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 sand- 

 stones and grit, and also many others of foreign origin, granite and 

 ti'ap being the most common. At Whinmoor, 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 ex- 

 tended as far south as the neighbourhood of Barnsley, for Prof. A. H. 

 Green has described a bed of glacial clay 3 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. Prom 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 of an ice-sheet which probably had its termination 

 in this district, and being thin could not exert a very great influence 

 in grinding up the rocks over which it passed. The greater part of 

 the Boulder-clay so deposited has since been removed by denudation. 



The glacier, whose existence is thus indicated, descended from the 

 northwards, and consequently must have crossed the lower part of 

 the valley of the Calder in the neighbourhood of the place where 

 Wakefield now stands, and several miles west of its confluence with 

 the Aire at Castleford. The facts already stated, though very briefly, 

 go to prove that on the recession of the glaciers which once 

 enveloped the country north of the hills separating the Calder from 

 the Aire, immense quantities of stiff glacial clay, filled with sub- 

 angular, scratched boulders of both local and distant origin, were left 

 filling up the valleys. The land appears at this period to have been 



1 Memoir of the Geological Survey illustrating Sheet 93 N.W. p. 14. 



2 Proc. York Geol. and Polyt. Soc. 1876, new series, pt. iii. p. 122. 



