J. W. Davis — Erratic Boulders of the Calder Valley. 317 



angular, and have all been derived from the neighbouring hills. 

 Granites, limestones, or other travelled boulders, do not appear to 

 be present. Some distance lower down the valley, as Burnley is 

 approached, however, the travelled boulders become common. 



If the erratics in the bed of the Yorkshire Calder were derived 

 from the Boulder-clays east and north-east of Burnley, it is quite 

 evident that they could not have been transported by river action. 

 The great rise to the summit of drainage disposes of that theory. 

 The only agent equal to the task appears to be drifting icebergs. 

 It is possible that large masses of ice may have been in existence in 

 the Burnley Valley, and these, becoming loose and floating away, 

 would carry with them any stones or boulders with which they 

 happened to be in contact. In order that these icebergs should be 

 able to float over into the valley of the Yorkshire Calder, it would be 

 necessary that the land should be lowered to the extent of between 

 750 and 800 feet, so that the sea might overflow the summit to a suf- 

 ficient depth to afford a passage for the ice-floes and their contents. 

 There are also other objections to this method of their entrance into 

 the valley ; amongst others, that the valley is entirely devoid of 

 erratic blocks or boulders for many miles from its source, and it is 

 only when the lower parts are reached, that they occur, and the 

 nearer the mouth of the valley, the more numerous are the boulders. 

 It might also be expected that some of the boulders would lie strewn 

 on the sides of the hills, bounding the valley ; but hitherto both the 

 hill-sides and their tops have proved entirely devoid of such evidence. 

 For eight or ten miles the deep valley does not present any sections 

 exposing erratic boulders. At some distance below Hebden Bridge, 

 Dr. Alexander 1 quotes Mr. Gibson as having found a few fragments 

 of granite or trap whilst the railway line was in process of con- 

 struction, and a few well-rounded boulders are occasionally found at 

 Mytholmroyd, two miles further down the valley, but they do not 

 occur in any considerable quantity until North Dean is reached. 



Turning next to the second source whence the Boulders may have 

 been derived, it is well known that the Valley of the River Ouse con- 

 tains immense quantities of Boulder-clay, Brick-earths, sands, and 

 gravels, derived from the glaciers which it has been shown descended 

 Swaledale and Wensleydale. The Boulder-clay may be con- 

 sidered as the foundation on which the others are deposited, and 

 where it has not been subjected to the action of water, still extends 

 across the whole breadth of the valley from the elevated Permian 

 Limestone plateau on the west to the Liassic and Oolitic wolds on 

 the east. Sections exposing the relative position of the series in the 

 valley are not frequently exposed. The Boulder-clay occurs exten- 

 sively east of Knaresborough, and southwards ; and on the opposite 

 side of the valley it is 60 or 80 feet thick near Easingwold. At 

 York the Boulder-clay is 70 feet thick, and the new railway station 

 works are all built on this material. South of the River Wharfe the 

 clay has a thickness of 60 feet. It contains immense quantities of 

 scratched stones, boulders of Mountain Limestone are numerous ; pink 



1 Proc. Geol. and Polyt. Soc. of the "W. Biding of Yorkshire, toI. i. p. 148. 



