Rei\ W. Lower Carter — Glaciation of Don Vuilei/s, etc. 549 



to a second invasion of the Don and Dearne A^alleys by ice, the 

 stream this time coming principally from the Tees. This glacier, 

 which had advanced down the central plain, was now, by the retreat 

 of the Pennine ice, enabled to push over the Aire-Don watershed 

 and Magnesian Limestone escarpment. Westwards it abutted against 

 the high land of WooUey Edge, and sent down a lobe of ice at 

 Staincross and Monk Bretton into the valley of the Dearne. This 

 second glacier does not, however, seem to have advanced far south 

 of the Barnsley-Advvick-Conisborough curve, and laid down the 

 upper clay of Staincross, the Shap granites of Royston and Adwick, 

 and the numerous Lake Country en-atics of the district to the north 

 and east of the Dearne. This glacier seems to liave advanced over 

 the Magnesian Limestone with a south-westerly movement, gradually 

 closing the gorge of the Don and carrying the material of denuded 

 Bunter and limestone beds over the escarpment to the south of 

 Conisborough, of which the pebble drifts are the relics. 



This movement does not appear to have extended much farther 

 southwards, as the Kiveton gorge seems to have presented a clear 

 course for the overflow of the lake formed by the damming back of 

 the drainage. The second glacier appears to have retreated north 

 of the Aire before the overflows at the head of Calderdale were in 

 full swing. The Don and Dearne valleys were therefore, in all 

 probability, clear of ice during the later part of the Glacial Period, 

 and have been subjected to enormous denudation, both during the 

 Glacial Period and since, which has cleared away the bulk of the 

 Boulder-clay and only left relics of previously widespread deposits. 



2. Glacial Lakes and Overflow Valleys. — Such a series of glacier 

 movements as has just been indicated would divert the normal 

 drainage of the district and produce lakes in the valleys thus 

 dammed up. The Boulder-clay at Ashfield's Pit, and near the 

 railway station at Conisborough, and at Cadeby, on the opposite 

 side of the Don, shows that this goi'ge must have been filled with 

 ice up to the 22o-foot contour. The scattered patches of drift from 

 Edlington to Clifton and Braithwell, reaching up to 400 feet, 

 indicate that the gorge was entirely closed above the 350-foot 

 contour. This is the general height of the Midland watershed of 

 the Don system, and is only broken through at one pomt south 

 of Conisborough, the Kiveton Valley (330 feet), near the middle of 

 which one of the sources of the river Eyton takes its rise. These 

 considerations warrant one in assuming the existence of a great 

 glacial lake, rising to the level of the 330-foot contour to the west 

 and south, and dammed back by ice from Conisborough to Barnsley. 

 This lake would overflow by the Kiveton gorge towards Worksop. 

 One cannot expect to find abundant evidences of lake deposits in an 

 area which has suffered so severely by denudation as this ; but the 

 geological surveyors map from 4 feet to 9 feet of brick-earth and 

 clay resting on gravel at Parkgate, and from 3 feet to 7 feet of brick- 

 earth near Wombwell. These indicate a lake both in the Don and 

 Dearne valleys, covering up the old river gravels. 



Following this line of argument, and taking the various patches 



