Vol. 67.] PERMIAN TO THE TRIAS IN NOTTINGHAMSHIRE. 101 



confirmed him in this opinion : he found no trace of a break 

 or unconformity within the red rocks — they seemed due to one 

 continuous deposition — and he felt compelled to carry down the 

 base-line of the Keuper to an horizon where the lithological 

 characters were marked and distinct, namely, to the junction with 

 the Durham Permian Limestone. At this horizon there is some 

 evidence of a possible unconformity. At Seaton Carew the red 

 rocks rest upon the upper division of the Limestone, which crops 

 out at Hartlepool. A boring on the north side of the Tees yielded 

 Axinus dubius and a roestone bed similar to one in the cliffs at 

 Hartlepool, indicating that the red rocks rest upon the same horizon 

 of the Limestone as at Seaton Carew. But, at the western outcrop 

 of the red rocks near Darlington, Leeming Lane, and llipon they 

 rest (with a thick bed of gypsum at the base) upon the fossiliferous 

 and compact limestone of the Durham Permian — that division 

 which immediately overlies the Marl Slate. Mr. Howell objected 

 to Wilson's description of the limestone at Saltholme as ' indurated 

 marl,' and gave an analysis showing that it contains over 95 per 

 cent, of carbonates of calcium and magnesium. He also quoted 

 Howse's view that this limestone and the accompanying marl are 

 identical with the Upper Limestone and Eed Marl of Sedgwick, 

 and the Brotherton Beds and Red Marl of Kirkby, as exposed at 

 Brotherton and other localities in South Yorkshire. 



Many other borings have been put down in the Durham salt- 

 district, which for the most part pass through strata similar to those 

 at Saltholme l ; but the only one requiring mention here is that at 

 Seaton Carew, mentioned above, which was made by Messrs. Case- 

 bourne & Co. in 1887. liock-salt was not met with in this case; but 

 the boring was continued into the Carboniferous, and proved that 

 the Magnesian Limestone was 878 feet thick. 



It appears from the conflicting evidence just adduced that nothing 

 is certainly known as to the age of the Salt Measures. The uncon- 

 formities which different geologists would place at different horizons 

 of the strata passed through by the boring seem to be fixed on purely 

 hypothetical grounds, except the one at the top of the Durham 

 Permian Limestone. That there is an unconformity in some parts 

 of England between the Keuper and the Bunter is probable, and in 

 fact detailed mapping indicates that this is the case near Nottingham. 

 The unconformity is, however, often assumed, in order to account 

 for the apparent absence of the Muschelkalk ; and it is far from 

 certain that this formation is not represented in parts of England 

 by sediments. Mr. Woodward 2 thinks that this is the case in 

 Devon, and, recently, Mr. Wills 3 has shown that certain beds which 

 have the appearance of Lower Keuper are not improbably of Letten- 

 kohle, or Muschelkalk, age. 



1 E. Wilson, 1888, p. 765. 



2 H. B. Woodward, 1874, p. 389. 



3 L. J. Wills, 1910, p. 268. 



