Vol. 70.] OF DTTBHAM MAGXESIAX LIMESTONES. 243 



Hartlepool, "Warren Cement-Works Boring. — Middle 

 Beds, associated with a mass of anhydrite and gypsum. 



XLIX. Very hard and compact dark-grey rock, embedded in and 

 impregnated with anhydrite, and containing stellate aggregates of 

 anhydrite-crystals. 



A stained section reveals the merest trace of calcite. The an- 

 hydrite occurs in big clear radiating crystals, often containing 

 slight dolomite-inclusions. The dolomite consists of closely-com- 

 pacted allotriomorphic grains with included impurities. It does 

 not develop rhombic outlines where it projects into anhydrite. 

 (See PI. XXXVII, fig. 1.) 



L. Beneath the anhydrite mass. Dark-grey rock with specks of 

 gy])surn, but no anhydrite. Traces of gasteropods, Strophcdosia, 

 and bryozoa occur. 



Stained sections reveal large dolomite-grains, both allotriomorphic 

 and idiornorphic, with faint dirt-inclusions — chiefly towards the 

 centres. Very little calcite is present ; but an occasional allotrio- 

 morphic crystal occurs, and it is seen separating out in strings. 

 Another more highly-gypsiferous section is made up of very small 

 allotriomorphic dolomite-grains, dark with inclusions. Grypsum 

 occurs in irregular patches, while the dolomite-crystals become 

 very much larger and clearer, and develop rhombic outlines where 

 they project into or lie in gypsum. (See PL XXXVI, fig. 1.) 



XLIX. L. 



Insoluble residue 1'93 2*32 



Water, etc — 0*61 



FeO, etc. 0-75 0-83 



CaC0 3 38-30 49'33 



MgC0 3 32-16 39-50 



CaS0 4 ' 27-85 7-58 



Totals 100-99 100-17 



Calcite 0'02 2-30 



Dolomite 70'44 86-53 



Bedded Middle Series, on the Eastern side of the 

 Shell-Limestone. 



The structure of these beds is now almost completely masked 

 by the changes which they have undergone. A considerable 

 mass of thickly-bedded dolomitic rock occurs beneath the Flexible 

 Limestone in the coast-section between Ryhope and Sunderland, 

 in which spongy calcareous structures are developed only to a 

 moderate degree. Otherwise I have seen but three very definite 

 patches of original material, all of which were analysed. 



The lowest part of this division at Trow Rocks includes a 

 considerable extent of the true 'cellular rock,' resting directly 

 upon well-bedded Lower Limestones. The line of demarcation 



