312 DR. D. W00LAC0TT ON THE STRATIGRAPHY [Aug. I9II, 



11. The Stratigraphy and Tectonics of the Permian of Durham 

 (Northern Area). By David Woolacott, D.Sc, F.G.S. 

 (Bead April 5th, 1911.) 



[Abstract.] 



The Permian strata of Durham and Northumberland lie uncon- 

 formablj on a basin of the Coal Measures. They can be divided as 

 follows : — 



(4) Upper red beds, with salt and thin f ossiliferous mag- 

 nesia n limestones (only exposed in the south of Durham). 

 300 feet. 

 (3) The Magnesian Limestone. 

 («) Upper. 



1. Yellow bedded limestone of Eoker. 100 feet. 



2. The concretionax-y limestone of Fulwell and Marsden — a series of 



concretionary and non-concretionary limestones and marls. 150 to 

 250 feet. 



3. The Flexible Limestone. 10 to 12 feet. 



(b) Middle. 



Unbedded (as a rule), highly ^ 



fossiliferous (often) lime- | ( Bedded yellow, non- 

 stone of Claxheugh, Tun- . , I fossiliferous limestones 

 stall, etc. Forms a ridge | re P _j* | of the northern end 

 of high ground, and reaches ! ,, J of Marsden Bay and 

 a thickness of 300 feet. | _? ] the coast from Hendon 



Often brecciated and en- I , to Seaham Harbour, 



tirely changed in character J ' Often highly brecciated 



■ — rendered more calcareous j ^ 150 feet, 



and fossils obliterated. J 



(c) Lower. Bedded brown limestones of Frenchman's Bay, Houghton 



etc. Upper beds often disturbed. 40 to 200 feet. 



(2) The Marl Slate. 3 feet. 



(1) The Yellow Sands, from to 150 feet. 



These beds, which vary much in thickness, lie in North Durham 

 in the general form of a syncline beneath Sunderland. 



The unfossiliferous Yellow Sands are probably a deltaic formation 

 reassorted by wind, the other beds being the result of deposition in 

 an inland sea undergoing desiccation. The magnesium carbonate 

 existed in the waters of the sea, and was either deposited along 

 with the calcium carbonate, or introduced by seepage when the beds 

 were being laid down. 



Great changes in the amount and distribution of these carbonates 

 have, however, taken place since deposition. The cellular structures 

 that occur in the limestone can be classified as follows : — (1) Con- 

 cretionary-cellular ; (2) negative breccia ; (3) solution-cavities ; 

 and (4) fractured cellular. Most of them have been produced by 

 the leaching-out of the magnesium carbonate (dedolomitization), 

 or of both that and calcium carbonate. In some cases the rock 



