326 Exposmrs of Glacial Drift at Doiicastcr and Tickhill. 



sand, and is covered b)' 80 feet of alliuial clays, sands, and 

 gravels. The boulders contained in it are principally of Permian 

 Limestone. There are a few Carboniferous grits and ganisters, 

 and some finely scratched Carboniferous close-grained, and also 

 encrinital, limestones. Several specimens have been found of 

 Coal Measure shale with Anthracomya Phillipsi. Shales with 

 this characteristic Upper Coal Measure fossil are also found in 

 the Balby clay. The beds from which these shales may have 

 been derived are not known to occur in Yorkshire further north 

 than the Don valley. The presence of this fossil in the Balby 

 and Bentley clays lends support to Mr. W. Lower Carter's 

 suggestion that ice passed west of the Permian escarpment, and 

 then entered the lower levels by way of the Don gorge. 



In a distance of two miles between Wadworth and Tickhill, 

 the South Yorkshire Joint Railway is making four cuttings 

 through boulder clay. The most southern of these is at All 

 Hallows Hill, which is near Tickhill, and a little over six miles 

 south of Doncaster. Where the base of the clay is seen it rests 

 on Upper Permian or Triassic sands and marls. In the inter- 

 secting valleys the fossiliferous top beds of the Upper Permian 

 Limestone reach the surface. In its deepest part the clay is 

 more than 20 feet thick, the base not being exposed. In the 

 first three cuttings it is not as tough as at Balby, but at All 

 Hallows Hill it is so stiff that the railway contractor is using 

 explosives for the purpose of excavating it. The boulders are 

 mainly of Permian Limestone, and range up to 12 cubic feet in 

 size. There are Carboniferous limestones up to two feet cube, 

 some of them being highly fossiliferous. In addition to encrinital 

 blocks there are large pieces containing Producfus Cora, P. 

 scabricido-costatus, P. longispinus, and Aviculopccten. There are 

 also Carboniferous grits and ganisters, and a few Lake District 

 boulders. The stones are sub-angular, and are well scratched. 

 No traces of the Coal Measure shell beds, such as are seen at 

 Balby and Bentley, have been found in these deposits. 



Like the Balby clay the Wadworth and Tickhill deposits are 

 closely packed on the low western rim of the southern extension 

 of the Vale of York. The positions they occupy on the gentle 

 slopes of the hills have shielded them from denudation, and it is 

 more than probable that they are the relics of a widely extended 

 moraine. The plain which lies below them to the east stretches 

 beyond the Trent, and except where broken h\ the low escarp- 

 ments of the Bunter and the Keuper, is for the most part below 

 the 25 feet contour. It is bounded on the south by the range 



Naturalist, 



