23 
writers) ; strongly heated vapour escaping througli crevices 
in the coal, which are due to undulations of the strata 
{Rogers^ Fennsykania II. y ii, p. 809) ; evaporation through 
faults, with or without heat {LyelVs Travels in North America^ 
vol. ii) 
The mode of occurrence of Anthracite in South "Wales and 
Pennsylvania was described. The gradual debitumenization 
of the coal westward in South "Wales and south-eastward in 
Pennsylvania was discussed with reference to the great lines 
of disturbance. 
Cases of coal altered in texture, cleavage, and proportion 
of volatile matter by approach to open faults were cited. 
Details were given of one case in the Black Bed Coal at 
Cleckheaton, where the coal lost its cubical fracture com- 
pletely, and from 8 to 14 per cent, of its volatile matter on 
approaching an imperfectly sealed fault. 
Experiments, suggested by this circumstance, had been 
instituted by the author, and various kinds of coal powdered 
and exposed to the air were found to lose from 4 to 17 per 
cent, of their volatile constituents in two months' time. 
The highest proportion resulted from an experiment on Low 
Moor Better Bed coal. 
The quantity of volatile matter in coal covered by a sand- 
stone roof is usually much diminished. This was attributed 
by the author to evaporation through a comparatively porous 
rock* Many cases of great accumulations of coal-gas in 
fissures or cavities in the coal were then cited. 
The recent experiments of Grundmann of Tamowitz and 
Varrentrapp of Brunswick were quoted, but the author had 
been unable to reproduce their experiments. The tempera- 
ture employed by them is not stated ; perhaps it was higher 
than the ordinary temperature to which the powdered coal 
was exposed in the author's experiments (Mean of two 
months, June and July = 61°). 
