Vol. 70.] OF DUKHAM MAGNESIAS LIMESTONES. 247 



Lower Limestones. 



Blackhall Colliery Sinking. — A yellow, well-bedded, 

 friable, nodular rock, with loose powdery material between the 

 harder nodular parts. No fossils. 



LXII. The fine incoherent powder. 



LXIII. The harder nodular portion, freed from the above by 

 washing. 



LXII. LXIII. 



Insoluble residue 0*21 0*18 



Fe.,0 3 , etc 0'42 0-13 



CaCO, 54-95 55-43 



MgC0 3 45-27 45-05 



Totals 100-85 100-79 



Calcite 1'05 1-80 



Dolomite 99-17 98*68 



LXIV. Near the top of the Lower Limestone. Yellowish-white, 

 well-bedded, rather soft rock with carbonaceous partings. Com- 

 minuted bryozoa and plant-fragments occur. 



LXV. A very white, dense, compact, fine-grained, bedded rock 

 without cavities. No fossils. 



LXVI. Near the base of the Lower Limestone. Hard, dark- 

 grey, compact bedded rock, with irregular carbonaceous partings. 

 Cavities, lined with a few small crystals of pyrite and calcite, 

 occur along the bedding-planes. No fossils. 



Stained sections of the last two rocks show small, closely- 

 compacted, allotriomorphic dolomite -grains, dark with inclusions 

 of ferruginous matter, pyrite-grains, etc. A general stain ovei 

 No. LXVI shows the presence of a good deal of calcite, gathered 

 round the margins of the dolomite-aggregates, and also along 

 straight lines passing in various directions. No. LXV shows less 

 calcite, but the mineral is similarly distributed. 



LXIV. LXV. LXVI. 



Insoluble residue 0*15 0-12 1-01 



Fe 2 3 , etc 0-59 0-22 2-22 



CaC0 3 55-01 55-29 54-94 



MgCO 44-78 45-18 42-35 



S0 3 0-08 0-03 0-14 



Totals 100-61 100-84 100-66 



Calcite 1'70 1-50 4-52 



Dolomite 98-09 98-97 92-77 



Thickley Quarry, near Shildon. — LXVII. A smoke-grey, 

 fine-grained, compact rock enclosing numerous well-preserved fossils, 

 such as Productus, Spirifer, etc. This calcareous rock is regularly 

 bedded, with little trace of internal movement. 



LXVIII. Shell of Product-its from the above-described rock. 

 Q. J. G. S. No. 278. s 



