THE PERMIAN FORMATION. 189 



character of the " Dolomitic Limestone, '' from actual examination of 

 the cores, and that we may accept his statement on this point. Not 

 having seen these cores myself, I cannot express a decided opinion 

 thereon. A priori, however, there would appear to be a much greater 

 probability of these beds of Rock Salt, Gypsum, and (?) Limestone, 

 belonging to the overlying Salt bearing and Gypsiferous Keuper Marls 

 than to the Permian Rocks. 



In South Yorkshire the Magnesian Limestone consists of the follow- 

 ing subdivisions : — <a) 



Lower Magnesian Limestone consisting of : — 



I. — Lower Limestone. — Light coloured, thick or thin bedded, oolitic 

 or crystalline Limestone with thin marl partings, occasionallv ripple 

 marked. Mr. Kirkby describes thirty-one species of fossils from these 

 beds. The fewness of the species is, to a certain extent, made up by 

 number of individuals. Some of the beds are almost entirely composed 

 of comminuted polyzoa. Only eleven of the thirty-one species or one- 

 third are common to the compact Limestone (the lowest division of 

 the Magnesian Limestone) of Durham, though all the species but two 

 of this Lower Limestone of Yorkshire are found in the middle division 

 (viz., the Shell Limestone) in Durham. Estimated thickness, 120ft. 



II. — Small Grained Dolomite. — Light coloured crystalline or compact 

 Limestone, with thin clay partings, irregularly stratified and apparently 

 extensively false bedded. This rock is practically unfossiliferous. 

 Estimated thickness, 200ft. It comes above the Lower Limestone. 



Middle Marls. — Variously coloured marls, and soft sandstones, with 

 thin seams of gypsutn. These marls are very fluctuating in their dis- 

 tribution. According to Sedgwick they have not been found in the 

 Magnesian Limestone north of the Wharfe ; and south of that river 

 they are also sometimes absent, in which case the Upper Limestone 

 (Brotherton Beds) rest directly on the Lower Magnesian Limestone, 

 as for instance, in the neighbourhood of Tadcaster. ibj Thickness, 

 50ft. to 30ft. or less. 



/• Limestone or Brotherton Beds. — Thinly bedded Limestones, 

 white or grey, red or yellow in colour, containing little or no magnesia, 

 and with thin marl partings, containing ripple marks and sun cracks. 

 The fossils are limited to a very few species, viz.. Myalina Hausmanni, 

 Axinus dubius, and Acanthocladia anceps. Thickness, 30ft. to 120ft. 



Upper Permian Marls. — This is a thin and fluctuating deposit in 

 Yorkshire. It consists of beds of similar lithological character to the 

 Middle Marls. It has but a small surface extension, being very generally 

 overlapped by Triassic Rocks. Its maximum known thickness is 

 50ft. 



(a) Notes on the Permian Kocks of South Yorkshire, and on their palseonto- 

 logical relations, by J. \V. Kirkby. Q.J.G.S., vol. svii., p. 287. 



(b) The Permian and Triassic Kocks about Tadcaster. Mem. Geol. Survey 

 Bee Map 93 S.W. 





