STEVENSON, COAL BASIN OF COMMENTRY 
173 
along the strike and faulted in at least two places. The Banc des Brouil- 
lages is shown on the easterly wall. 
The conditions between the present workings and the original outcrop 
cannot be ascertained now, as the rocks have been removed, but Fayol 1 
reports that some beds of shale seen, when he wrote, at the bottom of l’Espe- 
rance, thickened and multiplied toward the outcrop so that,within 200 meters, 
the great coal bed was changed into a mass of shale, sandstone and coarse 
conglomerate, containing much bituminous shale but no workable coal in its 
18 meters of thickness. It would seem then that the Brouillages condition 
prevailed, at the outcrop, throughout the whole thickness of the deposit; 
that the petty lenses of sand and clay, observed in the Banc inferieur, are the 
last traces of detrital beds thickening toward the north and northeast. 
Returning now to the westerly wall of the excavation, the Grande Couche, 
where last seen at the bottom of that wall, shows approximately 18 feet of 
coal above the Banc des Roseaux, the Banc des Chavais having disappeared. 
The dip, not easily determined, is not far from 20 degrees and at one time 
the coal was overlain by a grayish shale, of which a little remains in contact 
with the westerly wall. But the coal with most of this shale has been 
removed as by a thrust, and on the planed off surface there now rests uncon- 
formably a dark shale, wholly unlike that of the wall. The condition is 
shown in Plate XVI, figure 1, where the plane of contact and the overlying 
shales are sufficiently distinct, although as the exposure was in shadow, the 
details are somewhat obscure. Before considering this matter further, the 
features of the westerly wall, as exhibited in Plate XVI, figure 2, must be con¬ 
sidered. 
The reader will remember that in the Saint-Edmond a sandstone group 
was seen, which thinned westwardly and disappeared near the head of Foret, 
so that the basal sandstone of the Gres Noirs, belonging above the top of 
the Saint-Edmond wall, is present in that of Foret at not more than 80 feet 
above the Grande Couche. This interval remains practically unchanged 
along the outcrop into l’Esperance, a distance as great as the whole length of 
Foret. At the entrance to l’Esperance, the basal sandstone of the Gres 
Noirs is soft, by no means coarse and directly overlying a thin bed of coal. 
It is, as in Foret, an irregular deposit, with streaks and pockets of coal. 
The shales below the little coal bed to within 25 feet of the Grande Couche 
are more or less sandy, light gray and with layers of soft white sandstone, 
which are distinct along the wall and some of them appear in the photograph. 
The little coal bed about 70 feet above the main coal at the stairway 
descends irregularly along the wall for about two thirds of the distance and 
1 Commentry, p. 241. 
