MESSRS. BAKEK AND XATE's NEW FLORA; 359 



Another point to which I would refer is the statement that 

 the western escarpment of the Magnesian Limestone, in passing 

 across the Coal-Measures, forms a broken line of eminences of 

 nearly equal height throughout. The height of the escarpment 

 certainly is never very great, but it is subject to considerable 

 variation of level. From South Shields to West Boldon it 

 ranges from under 100 to 300 feet ; thence to Thrislington, 

 from 800 to 550 feet ; then on to Westerton, where it attains 

 the height of 644 feet ; afterwards by Eldon (540 feet) to East 

 Thickley, w^here it is about 400 feet ; from this point it rises 

 again to 650 feet to the W. of Redworth where it is highest, and 

 where the Coal-Measures appear to run out, though to the south 

 of these the elevation of the escarpment or western termination 

 of the limestone descends to 220 feet at Pierce Bridge. 



The Marl Slate ought scarcely to be described as slightly mag- 

 nesian when it has been shown by Mr. E. J. J. Browell to contain 

 from 12 to 39 per cent, of Carbonate of Magnesia. Eighteen 

 species have been described as found in this deposit. 



In the compact limestone of Mr. Tate over sixty species have 

 occurred instead of eighteen as mentioned. A list of thirty- 

 three species is given in the Quarterly Journal of Geo. Soc, 

 Vol. XVI. (1861), p. 318 ; and the discovery of additional spe- 

 cies is noticed in Nat. Hist. Trans. Northum. and Durham, Vol. I. 



The concretionary and pseudo-hrecciatecl limestones are de- 

 scribed as containing molluscs, corals, fish of the genera Palaio- 

 niscus and Acrolepis, a Calamite, and other obscure plants. It 

 is difficult to say what beds Mr. Tate intends to include in this 

 his fouith group, as he refers to no localities where they may 

 be seen. Professor King, in his arrangement of the same series 

 of rocks, has a brecciated and pseudo-brecciated limestone for 

 his second subdivision. Perhaps it is to this limestone that 

 the author refers ; but it, strictly speaking, contains neither 

 corals nor shells, nor yet fish or plants. It is essentially an 

 unfossiliferous deposit if taken alone, as by Professor King. 

 The only examples of Palceoniscus, Acrolepis, and Calamites, that 

 occur above the Marl Slate have been found in the higher beds 

 of the Magnesian Limestone, or in the fifth gi'oup of Mr. Tate. 



