74 Professor Harkness on Mineral Charcoal. 



together, it will easily be perceived that this association is the 

 result of partial drifting, since we have mineral charcoal so 

 combined that, although each separate piece has its fibres 

 parallel, the whole of the pieces are confusedly heaped to- 

 gether. 



This partial drifting of the matter which now occurs in the 

 form of mineral charcoal is borne out by other circumstances, 

 which at once show that this substance must, to a certain ex- 

 tent, be regarded as an accidental feature in coal. Among 

 these circumstances, we find the evidence afforded by the in- 

 terculated strata is such as to justify the conclusion that 

 when this mineral charcoal makes its appearance in consi- 

 derable masses in a fibrous state, it owes its position to partial 

 drifting. 



In the sections given by Mr Dawson of the coal-measures 

 of South Joggins, Nova Scotia {Quart. Jour. Geol. Soc, 

 Vol. X., p. 3), we have two instances given of the occurrence 

 of mineral charcoal, and in both of these the nature of the 

 accompanying deposits is such as to indicate the operation of 

 drifting causes. 



In the first instance, we have a " coal, with much mineral 

 charcoal," 8 inches thick, lying upon " under-clay, hard and 

 arenaceous," 3 feet in thickness, a description of floor which 

 shows considerable motion in the water from whence it ema- 

 nated. The second instance furnishes us with " coal and 

 bituminous shale, prostrate trunks of trees, and mineral char- 

 coal,''' half-an-inch in thickness, resting on " sandstone with 

 clay partings," also indicating the prevalence of motion 

 during the deposition of this bed containing mineral charcoal. 



The coal-fields of Great Britain, likewise, provide us with 

 proofs that this matter also occurs among the coal in conse- 

 quence of partial drifting. As an instance of this, in two 

 coal-seams which are wrought near Sanquhar, in Dumfries- 

 shire, where the great coal-field of Scotland has its most 

 southerly limit, we meet with the same causes influencing the 

 appearance of mineral charcoal. 



Here we have a coal called the Calmstone-seam, from the 

 circumstance that its roof is formed of fine indurated light- 

 grey clay, a deposit which must have sprung from a compara- 

 tively tranquil medium, and in this coal we have few traces of 



