58 SECTIONAL ADDRESSES. 



three or four interirodes. But if recognisable plant-remains are scarce, 

 it is far otherwise with remains of animals. Scales, teeth, and bones of 

 fishes are almost invariably present, and it is from cannel that our largest 

 collections of Coal Measure vertebrates have been obtained. Amphibian 

 remains are more rare ; Ostracods, such as Beyrichia arcuata, are 

 crowded in some planes, and lastly, fresh-water shells such as Carboni- 

 cola are represented commonly not by the shells themselves, but by 

 the flattened wrinkled epidermis, the calcareous shell having evidently 

 been dissolved by the acids generated by decomposing vegetable matter. 

 The texture of cannel is usually smooth and the fracture conchoidal in 

 the purest specimens, but in most cases it graduates into a black 

 carbonaceous shale. The ash content is always high, rising to 40 per 

 cent, before reaching the point at which it would be regarded as shale. 

 Chemically it is distinguished by the high yield of hydrocarbons, obtained 

 on distillation either as mineral oil or as gas. For this reason, in days 

 before the invention of the incandescent mantle, cannel for enrichment 

 of gas of low illuminating power was in great demand, and commanded 

 so high a price that I have seen our most famous fish-bed worked when 

 it was only seven inches in thickness. All these characteristics of 

 cannel are consistent with the view that it originated from a mass of 

 vegetation macerated in pools of water somewhat after the manner of the 

 'retting ' of flax. Sometimes the cannel is in unconformable relation 

 to the underlying beds, as at the Abram Colliery, Wigan, where it 

 rests in one district upon true coal, and, in the course of about a mile, 

 encroaches first upon the coal, then upon its underclay, and, finally, 

 where seven feet in thickness, it rests upon a bed of shale underlying the 

 underclay. Green suggests that cannel consists of vegetable matter 

 which was drifted down into ponds or lakes and lay soaking until it 

 became reduced to pulp. 



Some modes of occurrence of cannel are of particular interest for 

 the light they throw upon Coal Measui'e conditions. Some beds are of 

 wide extent, having been traced over an area of several hundreds of 

 square miles; on the other hand, strips and patches of a fraction of an 

 acre occur, such as that at the foot of a fault in the Barrow Colliery, 

 which I interpret to indicate a depression in the coal-swamp which was 

 connected with some movement of the fault. An interesting relation 

 is often found to subsist between the total thickness of a coal-seam 

 and the presence of a local patch of cannel. It commonly happens that 

 the presence of a patch of cannel as a constituent of a coal-seam is 

 accompanied by an increased thickness, even out of proportion to the 

 magnitude of the cannel, and this irrespective of whether the cannel 

 is above, within, or below the true coal. It may be explained by the 

 fact that the process of fermentation by which the cannel was produced 

 reduced its volume more rapidly than the ordinary decay did that of the 

 adjacent peat, and so maintained a depression in which more plant 

 debris could accumulate ; but the ultimate effect of this fermentation 

 was a less complete loss of hydrocarbons, and consequently, both 

 because its contemporaneous loss was greater and its subsequent loss 

 was less, the presence of a cannel component increases the thickness 

 of a seam. 



