Vol. 70.] OF DURHAM MAGNESIAN LIMESTONES. 235 



II. LlTHOLOGY AXD COMPOSITION. 



South Durham Salt-Deposits. 



I.*Newcastle Chemical Works borehole, No. 1, on the 

 bank of the Tees opposite Middlesbrough. Depth about 1052 feet. 



A hard, grey, fetid, compact, partly oolitic, apparently thinly- 

 bedded rock, impregnated with gypsum. 1 



I. 



Insoluble residue 1 "05 



FeO, etc 0-46 



CaC0 3 53-41 



MgCCK 44-40 



CaSO." 1-14 



Total 100-46 



Calcite 0\54 Dolomite 97*27 



Highest Limestones. (Hartlepool and Roker Series.) 



II. Fulwell railway-cutting. — A very white, powdery, 

 well-bedded rock, containing friable siliceous concretions. No 

 fossils. The coarser siliceous material was removed by riddling. 



III. Hesleden Dene. — A thinly-bedded, very porous, white, 

 friable oolite, made up of small and irregular concentric grains. 

 Full of hollow casts of four species of Upper Limestone fossils. 



IV. Hesleden Dene. — A white, massive, friable, well-bedded 

 rock, containing fossils similar to those found m No. Ill, but less 

 plentifully. It is quarried as a building-stone. 



V. Hartlepool shore-section. — Massive well-bedded oolite. 

 No fossils occur, but the bed is closely associated with fossiliferous 

 Upper Limestones. 



VI. Seaham Harbour. — In a mass of rock isolated from the 

 cliff -section. A bed about 2 feet thick near the middle of the 

 section : it is a very small-grained oolite, each grain hollow in the 

 centre. This bed is full of empty stellate cavities. No fossils ; 

 but Schizodus and Liebea occurred in a bed immediately below it. 



A stained section shows this rock to have been originally a fine- 

 grained oolite, the nuclei being dissolved out, and the concentric 

 structure nearly obliterated by recrystallization of the dolomite in 

 small, irregular, allotriomorphic crystals. The presence of calcite is 

 shown by a faint general stain, but it does not occur in well-defined 

 crystals," (See PI. XXXVII, fig. 5.) 



1 The analysis is of the actual fragment in which Richard Howse detected 

 the three characteristic Upper Zechstein fossils — Schizodvs chtbius, Liebea 

 hausmanni, and Chondrites virgatus. See Nat. Hist. Trans. North. & Durham, 

 vol. x, pt. 2 (1890). 



