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IRONSTONES 



87 



128. — Indurated magnesian limestone, Pi 



Hall Bocks, Durham 



Mr 



Uppee 

 Gallery. 



129 and 129a. — Magnesian limestone. — Sully Island, 



jive miles south of Cardiff, Glamorganshire. 



Magnesian limestones or Dolomites consist of carbonate of 

 lime and carbonate of magnesia, in varying proportions. 

 The specimens 123 to 129 show that magnesian limestones 

 are of various geological ages. It is a lithological character, 

 having no essential relation to the geological date of the 

 rock. 



130. — Carbonate of lime and carbonate of magnesia. 

 Strontian, Argyleshire. 



Wall-case 43 



Ironstones and Iron Ores. 



The two lower shelves (131 to 175) contain ironstones. 



In the Coal Measures these occur in stratified bands and 

 nodules, generally in the shales of that formation. The 

 ?stone, inW oolitic iron ores lie generally diffused in various members of 



ferrug 



The iron of the Lower 



Green Sand is chiefly high up in that formation, and consists 

 generally of thin reticulating veins crossing in all directions 

 the sandy strata in which they lie. The tertiary ironstones 

 are chiefly nodular, the nodules lying mostly in clays or 

 clayey sands. Sometimes these nodules, as at Hengistbury 

 Head, are several yards in diameter. — A. C. R. 



131. — Argillaceous or clay ironstone, from the 



Crosstone beds Coal Measures. — Ironbridge, Salop. 



132 — Argillaceous or clay ironstone, " Pennystone 



band," from Coal Measures. 



133. — Clay ironstone, with veins 



Dale 



Coal Measures. 



Warwickshire 



f> 



134 — Clay ironstoxe, part of a nodular concretion from 

 the pipe-clay beds of the lower Bag/shot series. — Branksea 

 Island, near Poole, Dorset. Presented by Colonel Waugh. 





