CHRIO-IHST-A.!-, ^.UTICLES. 



I. — Thk Magnesian Limestone of Durham. 



By David Woolacott, D.Sc. F.G.S. 



(PLATE XII.) • 



Part II. 



The Divisions of the Limestone — The Thrusting in South-East Northumberland 

 and North-East Durham — The Breccias. 



1. Divisions of the Magnesian Limestone of Durham. 1 



East. 2 West. 



Upper Bed 

 Beds. 



Upper 



Limestones. 



The Flexible 

 Limestone. 



Middle 

 Limestones. 



Lower 



Limestones. 



Marls, red marly false-bedded sandstones, 

 thin fossiliferous dolomitic limestones, 

 and beds of salt, anhydrite, and gypsum, 

 300 feet (only occur in South Durham). 



Oolites (originally gypsiferous) 

 of Boker and Hartlepool, 

 100 feet. 



Gypsiferous oolites 

 (proved by boring 

 in South Durham) . 



Concretionary limestone, 

 250 feet of bedded con- 

 cretionary dolomitic 

 and calcareous 

 rock. 



12 feet. 



Yellow-bedded 

 dolomitic and 

 segregated lime- 

 stones, 150 to 

 200 feet. 



Unbedded dolo- 

 mitic and cal- 

 careous shell- 

 bank of Bryozoa 

 Beef, over 300 

 feet. 



Segregated limestones. 

 Dolomitic limestone. 

 Dolomitic oolite. 

 Granular oolite. 

 Fossiliferous dolomite. 4 

 240 feet. 



250 feet of bedded yellow dolomites and dolomitic limestones, 

 with which are interbedded in the south of the county 

 lenticles of grey calcareous limestone. These beds thin out 

 rapidly to the north of Sunderland. 



1 Gypsum and anhydrite were probably present on all horizons, as proved by 

 their presence throughout the limestone in the Seaton Carew boring. The 

 Lower Limestones were probably the least gypsiferous, the eastern equivalents 

 of the reef the most, while the segregated and concretionary rocks were in all 

 likelihood impregnated with gypsum, and the hollow oolites of Boker and 

 Hartlepool were originally gypsiferous. 



2 East and west refer to east and west of the reef. 



3 The exact nature of the original Upper Limestones is as yet unknown to 

 the west of the reef. They are totally denuded north of a line drawn through 

 Hartlepool. They have been passed through by borings in South Durham, but 

 nothing very definite can be gathered from the description of these. The 

 Upper Bed Beds occur to the west of the reef, and the Upper Limestones are 

 gypsiferous and in part oolitic. The concretionary limestones probably do 

 not occur, being represented by gypsiferous rocks. 



4 Maximum proved thickness as obtained in the Sheraton and Cotefield Close 

 borings. These beds are largely denuded in North Durham and in the south 

 of the county are covered by drift. 



