•202 Till PERMIAN FORMATION. 



together are only 66ffc. thick. Finally, at Nottingham, the Magnesias 

 Limestone dies out altogether. Whilst the calcareous members of the 

 formation attenuate on thesouth, the intervening sedimentary deposits 

 simultaneously expand. In Durham it is very problematical whether 

 the Upper Permian Marls are present, and if they are, they must be 

 intercalated with some thick bands of Limestone (see Middlesboro' 

 i In South Yorkshire these Upper Marls arc in places at 

 50ft. in thickness ; and at South Scarle, Lincolnshire, between 

 soft, ami 100ft. A middle series of Marls and Sandstones unknown 

 in Durham, or the North Biding of Yorkshire, become let in further 

 south between the Upper and Lower Limestones. In South York- 

 diddle Marls have a thickness of from 30ft. to 50ft.; and 

 ;it South Scarle of 140ft. The Marl Slates, which consist of a variable 



■ if Shales, Sandstones, and Limestones, of which the sedimentary 

 constituents on the whole predominate, in Durham vary from a yard 

 or so up to .(int. in thickness; and in Yorkshire, when visible along 

 the Magm sian Limestone escarpment, are not more than 10ft. or 12ft. in 

 thickness, but uinler parts of Notts (between Shireoaks and Mansfield) 



a thickness of from 50ft. to 150ft., and at South Scarle of well 

 oigh -JOOft. 



The accompanying diagram will roughly represent the mutual 

 interfacings of the calcareous and sedimentary members of the Permian 

 formation in the north-east of England. (See Fig. 3, Plate VIII.) 



Origin of the Permian Hocks of the North-f.ast of England. 



Professor Ramsay some years ago enunciated the theory that the 

 i i hi Limestone of England was formed in part, at least, by 



direct chemical precipitation in inland salt lakes, comparable, in some 

 tsto the Great Salt Lake of Utah, and in its restricted fauna 

 to the far greater salt lake of the Caspian Sea, and which lakes, like the 

 latter, may p issibly have been previously connected directly with the 

 open aea. (a) ."The Gypsum, the Dolomite or Magnesian Limestone, 

 the Red Marls covered with rain pittings, the suncracks and the 

 ions of the foot-prints of reptiles made on the soft, sandy 

 marls when the water was temporarily lowered by solar evaporation 

 in successive summers, all point to the fact that the Permian strata 

 were not deposited in the sea. but in a salt lake or salt lakes once for 

 a tine connected with the sea. (b> Dr. T. Sterry Hunt had already 

 indi pendentlj arrived at the same conclusion for all Magnesian Lime- 

 stones. According to that eminent physicist, Dolomites. Magnesites, 

 and Magnesian Marls have been formed by the evaporation of 

 solutions of bicarbonate of magnesia, which have been produced 

 either by the action of bicarbonate of lime upon solutions of sulphate 

 of magnesia (in which case gypsum is a subsidiary product) or by the 



On 1 • England of older date than the Trias," by A. O. 



Ramsay . i i. - <,< F.G.S., vol. m U„ p. 24. 



Presidential lddr< b to British Association, 1880, by A C. Ramsay, LL.D.. 



E K.S 



