DAVIS : FISH-REMAINS IN THE COAL-MEASURES. 43 
The cannel coal has here become diminished to two thin 
seams, 1 J inch and 1 inch thick respectively, and a little further 
eastwards, finally disappears, being replaced by a black 
bituminous shale. The stone coal is very fine-grained, 
bituminous, and of a dull black colour, lacking the shining 
fracture of the cannel of Lancashire. It is very homogeneous, 
and breaks with a concoidal fracture, mostly without a trace 
of the lines of deposition, and in this respect differing very 
much from common coal. The black bituminous shale, 
locally named "Drub" or "Hubb," is somewhat similar in 
appearance to the stone coal, and only differs from it in having 
a greater proportion of mud in its composition. It burns 
with a bright flame, and has been used in making gas for 
illuminating purposes, but leaves so very large percentage of 
ashes that it cannot be extensively used at the gasworks. In 
some instances it contains a quantity of mineral oil. 
From a consideration of the above facts we are naturally- 
led to think of the method of deposition of the substances 
forming the coal seam. The cannel coal being thickest in 
the centre, and thinning off in every direction, becoming less 
pure, and ultimately giving place to black carbonaceous shales, 
would appear to indicate that the plants were carried by 
streams into a quiet lake, where they became decomposed, 
and, settling to the bottom, accumulated as a homogeneous 
mass, prior to being changed by pressure and chemical causes 
into coal. The interlamination of shale, more frequent and 
thicker near the sides of the lake, would be the result of the 
mud, also brought by the streams, settling to the bottom 
quicker than the leaves and stems of the plants, but at the 
same time carrying down with it a good percentage of 
carbonaceous substances. Occasionally the lake appears 
to have been filled up, or elevated, above the water level, 
and seat earth, filled with rootlets of Stigmaria, has been the 
result. Above this are beds of ordinary coal, the plants 
