22(J 



NOTE ON 



JANASSA BITUMINOSA, SCHLOT., FROM 

 THE MARL SLATE, THICKLEY, DURHAM. 



JOHN COGGIN BROWN, B.Sc. 



' The outcrop of the Mag-nesian Limestone in South Durham 

 forms a fine, though not ver}^ elevated, escarpment facing- west- 

 ward and indented into a gTeat number of narrow bays by 

 denudation. The following places from north to south are in 

 the inland promontories of this escarpment, and serve to indicate 

 clearly the range of this singular rock [only those places in the 

 neighbourhood of Thickley are given]: — Merrington and Middle- 

 stone, Tottenham and Grange Hill, Eldon, Middridge and West 

 Thickley, Thickley, Redworth White House, Killerby, Headlam 

 and Piercebridge, where the formation crosses the Tees into 

 Yorkshire.'^ The section of the Permian rocks now exposed at 

 Thickley is not the common one. Usually the Magnesian Lime- 

 stone is underlain by the Marl Slate, under which the yellow 

 sands are found resting unconformably upon the surface of the 

 denuded Coal Measures. At Thickley, however, in the present 

 section the Yellow Sands are entirely wanting, the Marl Slate 

 resting directly and unconformably upon the surface of a hard 

 Coal Measure sandstone, as the accompanying photograph shows 

 (Plate XVHL, Fig. i). The Marl Slate here is also developed 

 on an unusual scale, being between five and six feet thick, and 

 composed of layers of a soft, yellow, flaggy arenaceous lime- 

 stone, which become somewhat harder near the top as they 

 approach the Magnesian Limestone, which is here very hard, of 

 a yellow colour, and contains some 19 general of the common 

 Permian fossils in one particular band first found by Calvert, but 

 now covered up. i As the section is made into the steep hill side 

 forming the outcrop of Permian formation it gradually exposes 

 from eight feet at the southern end to 30 feet at the northern 

 extremity. Over the lower portions — Marl Slate and Coal 

 Measure sandstone — there is a thick deposit of glacial drift which 

 contains some beds of sand. The Marl Slate of Thickley and 



*' Geology of Nortliumberlanci and Durham,' by Prof. G. A. Lebour, p. 34. 

 t' Zig--Zag' Rambling-s of a Naturalist. ' Manson. List of fossils from 

 Thickley. 



Geolog-y and Natural History of Durham,' Calvert, p. 74. 



Naturalist^ 



