Yol. 57.] seam: of coal into a seaji op dolomite. 303 



would be overlain by a sandstone, and as a matter of fact this 

 relation of coal to rock is found to hold in the majority of cases. 

 Sedimentation therefore was spasmodic ; it was at its maximum when 

 the sandstones were being formed, and it was approaching the 

 vanishing point when only vegetable matter, almost free from 

 mineral material, was being distributed. The dolomitic tufa of the 

 Wirral Colliery seems to carry us a stage farther. It was formed 

 on a spot to which clastic material scarcely gained access, and which 

 was reached even by vegetable matter in scant quantity and in 

 finely-divided form. 



The nearest approach to the spherulitic dolomite that I have 

 seen is a rock from North Staffordshire shewn to me by Mr. Gibson. 

 It occurs in bands and nodules in marls between the Deep Mine Iron- 

 stone and the Knowles Coal at Fenton Park, and was described by 

 Mr. Teall in the Summary of Progress of the Geological Survey for 

 1898, p. 127, as a sphaerosiderite (E 3214). In structure it closely 

 resembles the Cheshire spherulitic specimen, but differs in the sphe- 

 rulites consisting of carbonate of iron instead of dolomite, and in the 

 fact that coal fills the interstitial spaces in the Cheshire specimen. 



It has long heen known that coals are replaced by ironstones, and 

 ironstones by limestones. The origin of iron-ores by the replace- 

 ment of carbonate of lime has been proved in other rocks, but I am 

 unaware of satisfactory evidence that such was the history of any 

 of the Coal-Measure iron-ores. The Cheshire example is unique, 

 in the fact that the place of the coal is taken by dolomite, and that 

 the change takes place within a distance of a few yards. 



Chemical Aistalyses by William Pollakd, M.A., D.Sc, I'.G.S. 





E 3280. 



E3270. 



E 3344-45. 



Residue (ignited)^ 



Per cent, 



23-68 



0-34 



2-28 



0-33 



21-51 



14-33 



33-23 



4-09 



0-55 



trace 



Per cent. 

 11-02 



0-15 



0-60 



uot estimated 



26-21 



18-49 



40-49 



299 



0-45 



0-15 



Per cent. 



0-33 



0-34 



5-38 



0-33 



24-89 



13-23 



36-36 



17-80 



1-29 



0-70 



^l^Og-f trace of F^O 



FeO !... 



MnO 



CaO 



MeO 



CO2 



Coaly matter 



H2Oatl05° 



SO, 





Totals 



100-32 



100-55 



100-60 





Part insoluble in boiling dilute hydrochloric acid. 



