Vol. 70.] OE DUEHAM MAGNESIAN LIMESTONES. 237 



IX. X. XI. 



Insoluble residue 1'23 3*01 1-80 



Water, organic matter, etc. .. . tr. tr. 1*00 



FeO, etc. 0*18 0*60 0*75 



CaC0 3 89-23 82*91 56*00 



MgC0 3 9-60 13-65 40-06 



Totals 100-24 100-17 99-61 



Calcite 77'80 66-66 8*31 



Dolomite 21*03 29*90 87*75 



Fulwell Quarries, near Sunderland. — XII. Spherical 

 concretions, measuring about an inch and a half in diameter. 



Sections of the concretionary growths show very little structure. 

 If stained, rounded specks and fragments of dolomitic aggregates 

 with included impurities are seen embedded in a dense, finely- 

 crystalline, calcareous mass. The whole slide is frequently dark 

 with ferruginous and organic material. 



XIII. Yellow powdery matrix associated with the above, occu- 

 pying the spaces between the concretions. 



XIV. Aggregates of small concretions, about the size of peas. 



XV. Yellow powdery matrix, occupying the spaces between the 

 above. It can be washed away, or blown away with ease when dry. 



XVI. The ' Great Marl-Bed,' underlying the concretionary series. 

 A brown, friable marly rock. It shows traces of concretionary 

 action where it adjoins the overlying beds, but lower down the 

 concretionary action has been entirely arrested. 



A section shows patches of allotriomorphic calcite-grains arranged 

 in irreo-ular streaks in the dolomite, from which the calcite is 

 well separated. The dolomite develops rhombic outlines where 

 it projects into the calcite. The slide is full of ferruginous 

 and dirt inclusions ; and quartz and tourmaline-crystals can also 

 be seen. (See PI. XXXVI, fig. 5.) 



XII. XIII. XIV. XV. XVI. 



Insoluble residue ... 1*26 2*65 1*42 4*11 5*02 



Fe 2 3 , etc 0*45 1-26 0'47 1*22 2*41 



CaC0 3 90-35 55*37 88*13 55*62 55*69 



MgC0 3 7*90 40*97 10*22 39-81 35*80 



S0 3 0*21 0-23 tr. tr. tr. 



Totals 100-17 100-48 100-24 100*76 98*92 



Calcite 80*95 6*59 75*96 8*23 13*07 



Dolomite 17*30 89*75 22*39 87*20 78*42 



Byer's Quarry, near Marsden. 1 — Most of this quarry 

 consists of well-bedded, hard, calcareous, more or less distinctly 



1 Byer's Quarry is the chief locality for the fauna of the Upper Lime- 

 stones. The ' bluestones ' here are reputed to be the purest calcite in the 

 district. 



