502 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



ample, showing that there were many contemporaneous swamps, 

 separated by low divides ; their coals are at the same horizons but 

 conditions must have differed locally, for the coal is not the same in 

 all. The existence of such separated areas is distinct at many hori- 

 zons. The Canister Coal is present in the southern part of the field 

 but is wanting at the north. The Better Bed is very irregular at 

 the south but is important at the north. The Silkstone Coal is very 

 good near Cawthorne, but thence for a long distance it is badly 

 broken ; when the regular seam is reached again at this horizon, it 

 is of different character. More striking is the occurrence of petty 

 isolated swamps, occupying depressions on surface of great sand 

 heaps. Many seams are important only within very limited areas 

 and sometimes a whole group of coals disappears.^"* 



The composition of the coal in the several benches of a seam is 

 rarely the same and occasionally the dift'erence is notable. One 

 bench may yield semi-anthracite and another bituminous coal ; that 

 from one bench may be caking and that from another may be non- 

 caking. Variations of this type are so numerous as to be common- 

 place."^ Cannel, the "stone coal" or miners or, if it contain high 

 ash, "johnnies," is not rare. It has no definite position; it may be 

 at the top or bottom or in the middle of a seam ; a whole seam may 

 consist of cannel ; but in every case it is lenticular. 



The coal varies in thickness as well as in quality. A great many 

 seams are worthless because of ash or sulphur; even in any seam 

 one bench may be clean, another dirty ; the coal at one mine may be 

 excellent, at another near by, it may be unfit for use. Faux-mur 

 and faux-toit are characteristic, inferior coal at top or bottom or 

 both being reported from many locaHties. The faux-mur of the 

 Silkstone Coal is crowded with Stigmaria at one mine. The roof 

 of the Canister Coal has marine fossils in the shale as well as in the 

 " bulHons.""*' Marine fossils are in the roofs of several coals in 

 the Millstone Grit. These occur rarely in the Middle Coal Meas- 

 ures and the black shales containing them are thin."^ 



10* Op. cit., pp. 20, 21, 128, 242, 294, 300, 400, 410, 441 and many others. 



105 Op. cit., pp. 270, 271, 281, 382 and others. 



106 These have been studied by M. C. Stopes and D. M. S. Watson, Phil. 

 Trans. Roy. Soc. Ser. B, Vol. 200, 1908, pp. 167-208. 



lOT Green and Russell, op. cit, 40, 63, 70, 71, no, 230, etc. 



