Cotefield Close and Sheraton, Co. Durham. 169 



The unconformity between these series was distinctly marked at 

 Cotefield Close. The Permian beds were lying without any marked 

 dip, but the rocks below were dipping at about 1 in 4 (15°), probably 

 in a northerly direction. They were penetrated by the boring 

 for 470 feet. For about 370 feet they were a series of yellow, 

 brown, and red sandstones, and felspathic grits, alternating with 

 beds of grey, greenish, and reddish shales, and fireclays. A 

 fairly coarse conglomerate occurred near the top. At one point con- 

 temporaneous erosion of the shales had taken place, as fragments of 

 shale were interbedded with the sandstone, the laminations of the 

 pieces lying at various angles in regularly bedded sandstone. Inter- 

 bedded with this series were five thin seams of coal (the thickest 

 being 11 inches). Remains of the ordinary Coal-measure plants 

 were common in the shale, such as Lepidodendron, Stigmaria, 

 Catamites, but no trace of any characteristic fossil such as Aviculopeclen 

 papyraceus 1 was found. 



N t 4 - * S 



Diagrammatic Section showing Termination of the Coal-measures 

 in South Durham. 



1. Ganister Series : beds of sandstone, felspathic grits, shales, fireclays, 

 and thin coal-seams with beds of Ganister (G) at base. The sandstones 

 probably thicken northwards, and these beds on north side of fault are chiefly 

 sandstones. 



B. Brockwell Seam. 



2. Coal-measures. 



3. Yellow Sands thinning out southwards and overlaid by Marl Slate. 



4. Magnesian Limestone. Only the lower part of this bed is shown. 

 No attempt is made to draw the beds to an exact scale. 



F. Butterknowle Fault. 



* Approximate position of Cotefield Close borehole. 



t Approximate position of Sheraton borehole. 



The length of the section is about 4 miles. 



Below these rocks several beds of Ganister alternating with 

 beds of shale and finely bedded micaceous sandstone Avere proved. 

 The thickest bed was 4 feet, and was of the "pencil" variety. 

 The occurrence of this Ganister is of some interest, because the beds 

 between the Brockwell Seam and the Millstone Grit are called the 

 Ganister Series, and are taken as the equivalents of the true 

 Ganister-bearing rocks of Yorkshire and Lancashire. It is proved 



1 Professor Lebour found this fossil along with other marine fossils in beds 

 occupying a similar position to these at Whittonstall (Geol. Mag., 1878, 

 p. 144). 



