98 



STEVENSON— FORMATION OF COAL BEDS. 



[April i8, 



hard, grayish black and with a fracture more or less conchoidal ; 

 while that from the lower is black, lustrous and somewhat prismatic, 

 with some mineral charcoal. These coals were analyzed by A. S. 

 McCreath, who obtained as the average of several determinations 

 for each 



The fuel ratio for the top is i : 3.17 and that for the bottom is 1:2, 

 there being a difference of somewhat more than 9 per cent, in the 

 volatile matter. 



Gruner says that the Grande Masse of the Rive-de-Gier forma- 

 tion is double, the benches being separated by the " nerf blanc," a 

 white sand parting less than one third of an inch thick. The lower 

 bench or " rafford " is hard and dull, suitable for use in grates, but the 

 upper or " marechal " is tender, brilliant, less rich in oxygen and 

 employed in making gas and coke. There is very great variation in 

 the several parts of the Grande Couche at Decazeville but, according 

 to Fayol, the Grande Couche at Commentry seems to approach 

 homogeneity throughout. 



Barrois,^°* interested by the work of ^luck, Stainier, Strahan 

 and others bearing upon this question, secured analyses of the coal 

 from several beds near Aniche (Nord), the samples being taken for 

 each decimeter from roof to floor. The ash varied in one bed from 

 2 to 8 per cent. ; in another from 2.2 to almost 8 ; in a third, from 

 1.6 to 1 1.6 and in a fourth from i to 6.4 — the faux-toit and faux- 

 mur being neglected. The beds are thin, from 0.6 to i meter, and 

 the samples were taken without reference to the partings. The 

 results show definitively that conditions were not the same through- 

 out the accumulation of even a single bench. The volatile in dif- 

 ferent parts of a maigre coal varied 6 per cent, and in a demigras 

 coal, 8 per cent. 



^'^ C. Barrels, " Observations sur les variations de composition du charbon 

 dans certaines mines d'Aniche," Ann. Soc. Geol. du Nord, Vol. LX., 191 1, 

 pp. 177-186. 



