Stopes : Coal-balls found in Coal Seams. 337 



in this case seems beyond doubt) a seam containing- typical coal- 

 balls associated with goniatite nodules, which we have un- 

 earthed, lies some distance below the well-known Canister 

 bed, while the true Bullion seam lies above it. The pit at 

 Hough Hill, which has supplied so much material, seems also 

 to belong- to this lower horizon. Further, I have evidence of 

 very similar, if not identical, structures in the Middle Coal 

 Measures. This shows that the factors needed for the forma- 

 tion of these structures have combined more than once during 

 the deposition of the Coal Measures as a whole. The coal-balls 

 are undoubtedly concretions, largely composed of CaCOg, though 

 varying much locally, as detailed analysis shows. They are of 

 various sizes, and often completely surrounded by coal. As a 

 rule, the plants in two neighbouring balls are disconnected 

 fragments, but in some cases the same plant continues in two 

 nodules. This suggests that the concretions containing the 

 plant tissues were formed in the place in which they are now 

 found (except for slight subsequent shifting, due to earth 

 movements). Though this is opposed to Mr. Lomax's view, it 

 seems to be supported by the discovery at Shore of a single 

 calcareous mass, in the form of a number of nodules cemented 

 together by carbonates, all rich in preserved plant remains, 

 the whole enormous mass weighing two tons, and locally 

 replacing the coal in the seam. While further in support of 

 the in si/ie theory, a coal-ball found in the floor of the seam 

 contains practically nothing but stigmarian rootlets. The con- 

 stant association with the roof nodules containing marine shells 

 suggests that the infiltration of sea-water and carbonate was 

 necessary for the formation of the true ' coal-balls,' a view 

 suggested by Binney, against which we have as yet discovered 

 nothing directly militating, though we cannot give conclusive 

 facts in its favour. Experiments have been undertaken which 

 have conclusively shewn that sea -water and peat form a 

 splendidly preservative medium for plants^ though allowing 

 animal tissues to decay. A careful survey of the mine at Shore 

 reveals the extremely local occurrence of the coal-balls ; in 

 twenty yards a ' pocket ' may be worked through. The evidence 

 which could be collected under the difficult conditions of under- 

 ground work w^nt against rather than in support of the view 

 that they had been brought by streams at the time of the 

 deposition of the coal. Most of this work was done in collabora- 

 tion with Mr. James Lomax and Mr. D. M. S. Watson, though 

 our views do not coincide in all cases. 



1906 September i. 



