internal Structure of ike Magnesian Limestone. 115 



Bolsover ; probably exists in a state of minute subdivision in some earthy beds, which are liable 

 to effloresce. 



II. Green carbonate of copper — Very rare; a few fibrous veins about a tenth of an inch 

 thick, in a limestone near Newton Kyme ; in the same form at Farnham near Knaresborough*. 



III. Sidphurct of zinc— In small crystals imbedded in calcspar, contained in the hollows of 

 the marl-slate at Midderidge ; in the same form at Cowndon, with sulphate of barytesf • found 

 also by Mr. Winch nearly in the same form, and in the same part of the series at Cullercoats. 



IV. Sulphuret of lead — Found in several places, but generally in very small quantifies, in two 

 small strings traversing a white limestone under the milUdam south end of Mansfield • said also 

 to occur in the same form on the coast of Durham ; also at Whitley near Cullercoats ; in small 

 single crystals imbedded in the rock under Knaresborough ; in the same form in the upper lime- 

 stone at Oldcoats near Tickhill; in a similar form, and associated with sulphuret of zinc and sul- 

 phate of barytes, at Midderidge and Cowndon ; in large crystals and crystalline nodules sub. 

 ordinate to a small earthy bed at Nosterfield +. 



V. Carbonate of lime. — Rarely in thin fibrous beds, like those which alternate with the 

 Purbebk limestone ; frequently in large stalactitic masses occupying crevices and the sides of 

 small caverns, e. g. at J'arnham near Knaresborough, and in quarries in the outlier west of 



Collingham§; in contemporaneous veins; in crystals lining the cells of the regular beds. 



N.B. When these beds are magnesian, the crystals lining the cells generally exhibit the inverse 

 rhomb, rarely the equiaxe. But in the marl-slate, and other parts of the formation where the 

 magnesia disappears, the crystals lining the cells lose the rhombic form, and generally exhibit 

 modifications of the dog-tooth. In all the preceding instances, the crystals above described are 

 free from magnesia. There are, however, some rare instances of pearl spar subordinate to the 

 formation. 



VI. Sulphate of barytes. — A very abundant mineral in many parts of the formation. In cry- 

 stalline nodules and veins in the freestone beds of Mansfield and Huddlestone, &c. : in veins of 

 fibrous texture traversing beds of indurated marl, at Pleasley near Mansfield ; in contemporaneous 

 lamellar concretions, and also in veins in various parts of Bramham Moor. In small tabular 

 crystals, with carbonate of lime, in the cavities of the cellular beds of the same district ; also 

 massive and earthy in many similar localities; in kidney-shaped masses imbedded in marl, alter- 

 nating with magnesian limestone in the outlier west of CoIIingham. In many parts of the couu<y 

 of Durham, though not in the same abundance, it occurs in most of the preceding forms. 



VII. Sulphate of strontian. — A much more rare mineral, found of a fibrous and lamellar 

 structure traversing small veins in the yellow limestone near the left bank of the Nid above 

 Knaresborough ; said also to be found nearly in the same form in some quarries north of 

 Hartlepool ; in pale blue tabular crystals, associated with carbonate of lime in quarries south of 

 Ripon, &c. 



VIII. Sulphate of lime. — Though abounding in the lower red marl ||, it is very rare in the other 



* Traces of green carbonate of copper have, in a few instances, been left by the water which 

 springs from the magnesian limestone. In consequence probably of these appearances at Farn- 

 ham, considerable works were, about sixty years since, opened in (he yellow limestone imme- 

 diately behind the village ; but they were soon after deserted. 



t See p. 77, 78. X See p. 108. 



§ Some of the large specimens from this locality are beautifully translucent and fibrous ; and 

 among the successive layers of deposit exhibit curious traces of aggregation round different 

 centres. 



II No. 4. of the general section, p. 64. See also p. 101. 



q2 



