80 Professor J W. Gregory — Tlie English '' Eshers". 



III. Yorkshire. 



In Yorkshire esker-like formations are well developed at intervals 

 near Carvill Lewis' line showing the moraine which he considered 

 to mark the limits of the English land ice. In the Bingley-Ilkley- 

 Shipley area the eskers belong to two series, a low level series on the 

 floor of the Aire valley and a high level series on the moors between 

 the Aire and Wharfe valleys. 



1 . The Low Level Karnes of the Aire Valley. — Some of the most 

 accessible of the low-level formations occur along the Aire valley, 

 and may be seen from the Midland Railway. They have been 

 briefly described by Green. ^ The drift mounds on the floor of the 

 valley occur at intervals from between Steeton and Silsden, where 

 a few small hummocks occur at the level of about 300 feet, past 

 Bingley, where they form a band of gravel mounds across the 

 valle}^, above and below Saltaire, to about half-way between 

 Charlestown and Tong Park. The sections that I have seen in these 

 gravels are poor. Just AV. of the first lock W. of Saltaire, north of 

 Wiggiesworth's Engineering Works, the mounds consist of 

 tumultuous gravels with many sandstone boulders 9 in. and some 

 2 feet in diameter. Some of the smaller boulders are of Carboniferous 

 limestone. Pebbles of black chert are abundant. The constituents 

 of the gravels are well rounded ; a few of the boulders show faceted 

 surfaces as if they had been glaciated, but I saw no strise on them, 

 nor evidence of transverse banding. The uppermost layer is crowded 

 with boulders and large pebbles, probably by the removal of the 

 lighter constituents during denudation. 



Further down the Aire Valley a bank of fluvioglacial gravel, but 

 with the pebbles more rolled and water- worn than those opposite 

 Wiggiesworth's, occurs on the N. side of the main road from Charles- 

 town to Tong Park and just W. of a by-road going S. across the 

 valley to Thackley. The bank projects as if it were the remains 

 of a barrier across the valley. The gravel is exposed in a pit on the 

 E. side of that by-road ; the pebbles are mainly of Carboniferous 

 sandstones and limestones. 



Green applied the term esker to the Aire Valley mounds, while 

 recognizing that their shapes were due to denudation and that they 

 were the remnants of larger masses of grave]. Green suggested 

 that they were formed as terminal moraines in which the material 

 had been shot into water, therein spread out as bedded gravel, 

 and subsequently denuded into mounds.^ This explanation seems 

 consistent with all the available evidence. As they were water- 

 deposited and were not directly dumped from the ice, they are not 

 moraines ; they were formed at intervals along the valley as aqueous 



1 Geol. Yorks. Coalfield, 187S, pp. 77.5, 779, and 782 ; Mem. Geo!. Surv., 

 92S.E., 1879, p. ]2. 



- Cavvill Lewis has doubtfully referred to the mounds at Bingley as part 

 of his terminal moraine, which he also suggests was possiblj' at Skipton 

 (op. cit., pp. 193, 239.) 



