THE PERMIAN FORMATION. 121 



THE PERMIAN FORMATION IN THE NORTH-EAST 

 OF ENGLAND, 



WITH SPECIAL, REFERENCE TO THE PHYSICAL CONDITIONS 

 UNDER WHICH THESE ROCKS WERE FORMED. 



BY E. WILSON, F.G.S. 



f Continued from page 101. j 



Maul Slatbs (Kupfer Schiefek.) 



The Marl Slates have long been known in Durham as a thin, but 

 characteristic set of beds, coming at the base of the Magnesian Lime- 

 stone, and also, though less eommonly, in Yorkshire, but in neither of 

 these counties have they been found to exceed a few feet, or at most 

 yards, in thickness. During the past five or six years, I have been 

 able not only to make out the presence of Marl Slates in Notts and 

 Lincolnshire below the Magnesian Limestone, but also to show that 

 beneath those counties they exist in, relatively speaking, considerable 

 force, attaining a physical importance hitherto unknown in this 

 country. In the North-east of England the Marl Slates occupy but a 

 small surface extension ; they are chiefly seen in the Magnesian 

 Limestone escarpment, being there saved from denudation by the 

 protecting cloak of limestone. 



In Durham the Marl Slates consist of a series of thin-bedded grey 

 limestones and shales. These beds are rarely more than a yard or so 

 in thickness, but at one place (East Thickley) as much as thirty feet. 

 They are sometimes entirely absent ; the rapid fluctuations of these 

 beds are evidently owing to their resting on an uneven floor of 

 carboniferous rocks. They contain many imperfectly preserved plant 

 remains, viz., Neuropteris Huttoniana, (King.) Caulerpa (?) Selagi- 

 noides, (Sternberg,) and Polysyphonia (?) Sternberg iana, (King,) and 

 occasionally a few mollusca of the species Nautilus Freieslebeni, 

 Lingula Credwri, Discina Konincki, and Myalina Hausmanni. The 

 most interesting fossils, however, that have been found in these rocks, 

 are the fishes of the genera Palseoniscus, Platysomus, Pygopterus, 

 Ccelacanthus, and Acrolepis, the labyrinthodont amphibian Lepidoto- 

 saurus Durfii, and the lacertilian reptiles, Proterosaurus Speneri and 

 P. Huxley i. 



In Yorkshire the Marl Slates seem hardly to have been noticed 

 hitherto. This is, I believe, due rather to the scarcity of exposures of 

 these beds and the want of diligent research than to their actual non- 

 existence beneath the Magnesian Limestone escarpment. Mr. Kirkby, 

 erroneously I think, paralleled the Lower Magnesian Limestone of 

 South Yorkshire with the Marl Slates (and compact limestone) of 

 Durham, and was of opinion that the Marl Slates had no special 

 representative in Yorkshire. Mr. Lucas observes that "in the long 

 interval between Leeds and Crakehall there are no sediments beneath 



