548 Rev. W. Lower Carter — Glaciation of Don Valleya, etc. 



This evidence points to glaciation from the north and north-east 

 by two movements of ice. Two distinct tills, separated by warp and 

 pockets of sand, are found at Staincross, the lower with Carboniterous 

 boulders and the upper with Lake Country rocks. The drift patches 

 are also of two kinds, one set being of a specially Carboniferous 

 type and the other rich in Lake Country rocks. It is the latter 

 type that forms the Conisborough and Balby clays. In the Balby 

 pits there is also found a large percentage of Middle Coal-measure 

 material, which forms a perplexing mixture to explain. 



The author suggests that there was a double glaciation of this 

 area early in the Glacial Period, first by Pennine ice, and secondlj' 

 by the Tees glacier. 



It seems probable that at the commencement of the Glacial Period, 

 before the Irish Sea was filled witli ice, the Pennine Chain was an 

 area of great snowfall, and extensive glaciers were formed in the 

 valleys of Western Yorkshire. These glaciers would probably send 

 down considerable streams of ice into the central plain, laden with 

 Mountain and Yoredale limestones, cherts, ganisters, and Car- 

 boniferous sandstones. As the Glacial Period advanced the pressure 

 of the Norwegian ice forced the Tees glacier into the Vale of Yurk, 

 and this in its turn would push back the Pennine ice into the 

 lowlands of Airedale and over the low watershed between the 

 Aire and Don, inside the Magnesian Limestone escarpment, where 

 it spreads out westwards and southwards as far as Staincross, 

 Rotherham, and Conisborough. This seems to have been the line 

 of farthest extent of this glacier, which, though it interfered for 

 a time with the drainage of the Don, does not appear to liave passed 

 through the gorge at Conisborough. 



The country south of Frickley has undergone extensive denudation 

 since the cutting of the Darfield gorge, and it seems probable that 

 this was eft'ected by this ice, and, on its northward retreat, by the 

 deflected drainage of the Aire and Calder, which, as its course 

 eastwards would still be blocked by the advancing Tees glacier, 

 would find a ready route of flow through Frickley gorge. Thus 

 a large quantity of Middle Coal-measures material must have been 

 carried through the Conisborough gorge into the plain at Doncaster, 

 and would probably be suitably situated for the second glacier to 

 carry forward to Balby. As it has been suggested that this material 

 might be due to a glacier moving down the valley of the Sheaf from 

 Dore and Totley, this question has been carefully considered. The 

 geological surveyors do not record any drift in the valley of the 

 Sheaf, and a careful search of the 6-inch contour maps has not 

 disclosed any valleys which could have carried oft" the drainage of 

 the upper Don if it had been obstructed by such a glacier at Shefiield. 

 It is therefore concluded that no glacier capable of advancing to 

 Conisborough was formed in the valley of the Sheaf. 



The retreat of the first glacier may have been due to a lessening 

 of the snowfall on the Pennine watershed, owing to the shifting of 

 the area of greatest precipitation to the west of the Pennine Chain 

 as the Irish Sea became filled with ice. The evidence, then, points 



