Cotefield Close and Sheraton, Co. Durham. 165 



Lower Magnesian Limestone. 286 feet thick. 



i. Hard yellow dense dolomitic rock. \ 



j. Ditto, brecciated, with sparry cavities, passing gradually down 



into Dolomitic 



k. Hard grey calcareous limestone, with carbonaceous partings and 



and calcite-filled geodes (about 5 feet), passing down into I Calcareous 



I. Brown dolomitic limestone, brecciated in places. About 7 feet. /"Lower 

 in. Calcareous grey limestone with sparry cavities. Limestone, 



n. Hard brown dolomite. 166 feet 



o. Calcareous grey limestone. 



p. Brown brecciated dolomite. / 



q. Hard brown dolomite, with patches of calcareous limestone. ^ Calcareous 

 r. Brown brecciated dolomite with sparry cavities. I Lower 



s. Hard grey calcareous rock, brecciated in places. j-Limestone, 



t. Hard grey calcareous rock with sparry geodes. I about 



u. Grey calcareous rock, brecciated in places. J 120 feet 



v. Hard dark laminated Marl Slate. 1 foot. Marl Slate 



w. Grey hard dark calcareous limestone. 3 inches. \ 



x. Coarse grit, small irregular chips and fragments of crinoidal "Yellow" 

 limestone and chert in a matrix of rounded quartz grains r Sands, 

 interspersed with pyrites crystals. 3 ft. 6 in. 



y. Grey sandstone with rounded grains. ' 



z. Grey shale, the rounded grains of the Yellow Sands impressed "\ Coal- 

 on the surface of the shale at the junction. /measures 

 Total thickness of Permian, 504 feet. 

 The first rock met with, under the drift was apparently in both of 

 the borings the Middle Magnesian Limestone, there being no trace of 

 the typical upper beds as they appear in the area nearer the coast, 

 such as the Hartlepool and Roker dolomites (dolomitic oolites and 

 soft yellow dolomite) with the typical fauna of the Upper Magnesian 

 Limestone, nor the Concretionary and the Cannon-ball Limestones, 

 nor the bed which I have taken as the base of the Upper Limestone 

 series, viz. the Flexible Limestone. These upper beds occur on the 

 east of the Shell Limestone reef and also on the top of the reef in 

 some places; for instance, Dr. Trechmann records the cannon-ball 

 limestone as occurring on the top of the Shell Limestone in the 

 Blackhall Colliery sinking. We are of opinjon that owing to the 

 shrinkage of the sea in later Permian times the upper beds were not 

 deposited much to the west of the Reef. 1 



In neither of the borings was any trace of the richly fossiliferous 

 Bryozoa Reef of the Shell Limestone found. At Blackhall Colliery 

 sinking 3J miles to the north-east nearly the full thickness of this 

 bed — 335 feet — was pierced, and Dr. Trechmann was able to study 

 the zones of it. s Both of these borings are west of the Reef and pass 

 through a series of beds which are the western equivalent of it. 

 The Sheraton boring is probably less than a mile from it. In Castle 

 Eden Dene, 3| miles to the north, rather high beds of the Reef are 

 exposed at Ivy Rock. They are here full of fossils and merge west- 

 wards into a fine-grained, very pure, dolomitic bedded rock, which if 



1 Woolacott, " Stratigraphy and Tectonics of the Permian of Durham 

 (Northern Area)": Proc. Univ. Durham Phil. Soc, vol. iv, pt. v, p. 268, 

 1911-12. Trechmann, " On the Lithology of certain Durham Limestones " : 

 Q.J.G.S., vol. lxx, p. 260, 1914. 



2 Q.J.G.S., vol. lxix, p. 213, 1913. 



