Yol. 67.] PERMIAN TO THE TRIAS IN NOTTINGHAMSHIRE. 



99 



(4) Durham County. 



Prof. Lebour 1 has recently classified the Permian and Trias in 

 this county as follows: — 



Perior, 



Formation. 



( Keuper Red Sandstones 

 Salt Measures and Marls passing 



(Trias above, < downwards into si- 



Upper Permian below), milar Permian Sand- 



L stones, etc. 



Magnesian Limestone. 



Marl Slate. 



Permian. 



Yellow Sands 

 (Quicksands). 



Character of Material. 



Mostly red rocks with deposits 

 of rock-salt, gypsum, an- 

 hydrite, and thin magnesian 

 limestones towards the 

 base. 



Often concretionary. 



Flaggy calcareous beds : fish- 

 remains. 



Generally yellow, but some- 

 times dark-coloured, more 

 or less incoherent, water- 

 hearing sandstone. 



Thickness 

 in feet. 



up to 

 1200 



up to 800 



up to 15 

 (usually 3) 



up to 104 



He remarks that the subdivision of the limestone is difficult, and 

 that the following scheme drawn up by the late It. Howse is only 

 tentative, although the best available up to the present : — 



(/) Upper yellow limestone and 

 (e) botryoidal limestone. 

 (d) Cellular limestone and 

 (c) shell limestone. 

 (b) Compact limestone and 

 (a) a conglomerate at the base. 



Upper Group (3). 

 Middle Group (2). 

 Lower Group (1). 



Here the Middle Marls of South Yorkshire have disappeared, 

 and are presumably represented by limestone. 



The Upper Group of Durham is lithologically very remarkable, 

 and contains the well-known concretionary limestone of the Durham 

 cliffs, 2 which cannot be matched in Yorkshire. 



The thickness of the Magnesian Limestone Series varies from 

 800 to as little as 299 feet at Whitehouse, Norton, and even this 

 small thickness contains shale, gypsum, and nearly 90 feet of 

 anhydrite. 3 



In Northumberland only the lower divisions of the Zechstein 

 are present. 



The Salt Measures above the Limestone are of great interest, 

 and there has been much discussion as to their age. According to 

 the Geological Survey map, the Magnesian Limestone is imme- 

 diately overlain by Keuper Waterst ones ; Prof. Hull 4 thinks that 

 the salt-rock proved in the Middlesbrough boring occupies the 

 geological position of that which occurs in Cheshire, Staffordshire, 



1 G. A. Lebour, ' Geology ' in the ' Victoria County History of Durham ' p. 2 

 (reprint). 



2 E. J. Garwood, 1891. 



3 T. Tate, 1892, p. 493. 



4 E. Hull, in Bell, 1887, p. 155. 



h2 



