EXPLANATION OF THE CLAXHEUGH SECTION. 213 



An Explanation of the Claxhetigh Section, Co. Durham. By 

 D. WooLAcoTT, M.Sc, F.G.S. 



INTRODUCTION. 



Claxheugh Rock is a cliff about one hundred feet high and 

 250 yards long, lying on the southern bank of the river 

 Wear, about two miles west of Sunderland. It is composed 

 entirely of Permian strata, except at the eastern end of the 

 section, where a north and south fault throwing about loo feet 

 west brings the Upper Coal Measures and Permian into juxta- 

 position. The base of the entire Permian part of the section 

 is formed by the Yellow Sands, which are succeeded at the 

 western end of the section by the Marl Slate, a compact, 

 regularly-bedded Magnesian Limestone (Lower Magnesian 

 Limestone, Howse), and a fossiliferous, unbedded, crystalline 

 limestone (Shell Limestone, Middle Magnesian Limestone, 

 Howse). The thicknesses exposed of these strata are : — 



Middle Limestone 40 feet. 



Lower Limestone 10 „ 



Marl Slate 2 „ 



Yellow Sands 60 „ 



At the eastern end of the section the Marl Slate and Lower 

 Limestone are absent, and the Middle Limestone rests in a 

 very irregular manner on the Yellow Sands. The nature of 

 the entire section is shown in Section L and the accompany- 

 ing photograph. Some authors have supposed this to be a 

 case of the thinning out of these two middle beds, but the 

 manner in which the beds terminate, and other evidence to be 

 afterwards noticed, controverts this view. Other authors 

 have conjectured that the Marl Slate and regularly-bedded 

 Magnesian Limestone were denuded before the deposition of 

 the Shell Limestone upon them, but the facts brought forward 

 in this paper prove this not to be so. It appears to be 

 specially important that an explanation of this section should 

 be given, as Claxheugh is one of the few places where the 

 four members of the Permian there exposed can be seen in 

 succession, 



