188 THE PERMIAN FORMATION. 



In Durham the Magnesian Limestone consists of the following 

 sub-divisions : — a ) 



I. — Lower Limestone ( = Compact Limestone of Sedgwick.) — Light- 

 coloured, compact, crystalline, or concretionary limestone, poorly 

 fossiliferous, (38 species;) estimated thickness, 200ft. 



II.— Middle Limestone ( = Shell and Cellular Limestone.) — Light- 

 coloured, irregularly bedded, compact or crystalline limestone. When 

 fossiliferous the Shell Limestone of Sedgwick and the Fossiliferous 

 Limestone of King ; when unfossiliferous, the Cellular Limestone of 

 Sedgwick and the Pseudo-brecciated of King. The Shell Limestone is 

 the most highly fossiliferous member of the series, yielding most of the 

 characteristic fossils of the formation (120 species ;) estimated thick- 

 ness, 200ft. 



EQ. — Upper Limestone. — This member consists of an upper portion, 

 compact, vesicular oolitic, and thin-bedded yellow limestone, and a 

 lower portion of light-coloured, compact, crystalline or concretionary, 

 thick or thin, bedded limestone. This rock contains but few fossils, 

 viz., Axinus dubius, Myalina Hausmanni, Turbo helicinus, Clidophorus 

 costatus, some entomostraca and foraminifera, also several species of 

 fish of the genera Palseoniscus and Acrolepis, which have been found 

 at one or two places on the coast, associated with the remains of 

 coniferous plants and calamites ; estimated thickness, 250ft. 



Upper Red Marls. 



It appears somewhat doubtful whether these beds are represented 

 in Durham. Mr. Kirkby has given them a thickness of 50ft. in that 

 county. 



At and near Middlesborough, on the south bank of the Tees, some 

 years ago (1803) two boreholes were put down, which, after imssiiig 

 through between 1,100 and 1,200 of Triassic rocks, gave the following 

 very interesting sections in what may be the uppermost beds of the 

 Permian formation at that spot : — 



Ft. Ft. 



Keuper Marls and Sandstones, j 

 with Beds of Kock Salt and } 1,175 



Keuper Marls. &c 1,190 



Gypsum...... """•■•{ Limestone and Red Sandstone ... 16 



Doloinitu! Limestone, upper) 

 part of Permian Strata (Bam- 07 ., . Salt ,,,, 



say) ) 



Q Wft5l£l$N& S s : I H Li - sto - with liock Salt _^ 



1,209 I 1,811 



Prof. Ramsay (b) quotes the former of these sections as evidence 

 of the occurrence of beds of Rock Salt in the Permian series of this 

 country. I suppose Prof. Ramsay has satisfied himself of the Permian 



(a) See Synopsis of the Geology of Durham and part of Northumberland, by 

 Messr. lid. Howse and .1. W, Kirkby, lsCi.i, to whom I am chiefly indebted for the 



information here fjivon. 



(b) Presidential Address to Hritish Association, 1880, by A. ('. Ramsay, LL.D., 

 F.K.S. 



