STEVENSON, COAL BASIN OF COMMENTRY 
167 
Tranchee de Foret. 
The eruptive rock just mentioned is present as a broad projecting dike 
on the surface between Saint-Edmond and the next trench, known as the 
Tranchee de Foret, which is not more than 400 feet farther along the outcrop. 
This long trench of Foret is reached by a shallower, narrower excavation, 
termed by the miners the “Tranchee du massif.” The only work in progress 
here is upon the lower part of the Grande Couehe, known as the Banc des 
Brouillages, of which mere traces were seen in Saint-Edmond. It consists of 
alternating beds of coal and rock, each from one to two feet thick and forms 
the northerly wall of the trench. This deposit would be ignored in the Appa¬ 
lachian field as commercially worthless, but at Commentry the coal is saved. 
The steep dip makes winning of the coal less expensive, as the upper part of 
the bed has been removed; the rocky plates are stripped off easily and the 
amount of coal obtained comes to some thousands of tons per acre. The 
sandstone below this bed is rather coarser than in Saint-Edmond. 
The Banc des Brouillages forms the northerly wall of Foret throughout. 
The dip of the beds, as shown in the easterly wall of the trench, varies little 
from 30 degrees and the succession seems to be regular. The Grande 
Couehe is well exposed, being mined in a long open cut as well as by two 
slopes. The succession is, descending: 
Feet Inches 
1. Shales .Not measured 
2. Coal . 0 0-6 
This, exposed in the wall at the end of the trench, is merely a 
lentil. In that wall it is six inches thick, but at 150 feet away 
along the southerly wall it is but one inch; within a few feet far¬ 
ther, it breaks into a line of isolated nodules and disappears. 
3. Shales .25 0 
Grayish, fine grained, mostly well laminated and some layers are 
almost fissile; in part, especially in the lower portion, these shales 
are carbonaceous and impressions of leaves are not rare. 
4. Coal; Banc du tuit or Banc superieur .5-6 0 
This is variable in thickness as well as in composition and shows 
pockets of shale in which are streaks of bright coal. The upper 
part is cannel shale or shaly cannel and it too contains streaks of 
bright coal. The passage to the overlying shale is very gradual and 
the coal as a whole is of inferior quality. 
5. Banc des Chavais, Banc noir of the miners .9 7 
No trace of this parting appears in Saint-Edmond. As seen here, 
it is an irregularly bedded deposit, containing great numbers of 
rock fragments, angular or rounded and from one to four inches 
across; lentils of coal are abundant, one inch to two feet long, but 
rarely more than two inches thick. The upper portion passes 
