168 



David Woolacott — Borings at 



Colliery, Sheraton, and Cotefield Close confirms the view that the 

 Yellow Sands die out in the South of Durham. This thinning out is 

 irregular hut continuous. The fragments of Lower Carboniferous 

 rocks occurring in the Yellow Sands, and the thinning out of this bed 

 southwards, prove that the ridge of Carboniferous rocks that lay to 

 the south was exposed at the time of the deposition of the basal beds 

 of the Permian, and was being denuded until rocks of the limestone 

 faeies were laid down. It is interesting to compare the Permian in 

 the boring at Cotefield Close with that at Sheraton about 1^- miles 

 to the north-east and at Blackhall Colliery 2 miles further in that 

 direction. Thicknesses are given in feet. 



While the boring was being put down at Cotefield Close, after 

 a depth of about 250 feet had been reached the air rushed in to the 

 borehole and at other times out of it. This it did for days at a time, 

 varying with the height of the barometer, and proving in a notice- 

 able manner the porous and cavernous nature of the Middle Magnesian 

 Limestone. 



Coal-measures (Cotefield Close). 



The borings at Cotefield Close and Sheraton entered the Coal- 

 measures at a depth of 278 and 3 1 1 feet respectively beneath sea-level. 

 As the line of the Butterknowle fault runs between them the Permian 

 here is not affected by this fracture, which has a considerable throw 

 to the south in the Coal-measures beneath. At Butterknowle, 

 20 miles to the west, this fault has a downthrow to the south of 

 from 80 to 90 fathoms. 1 



- 1 Kirkby & Duff, "Geology of Part of South Durham " : Nat. Hist. Trans, 

 of Northumberland and Durham, vol. iv, pt. i, 1871. 



