178 
ANNALS NEW YORK ACADEMY OF SCIENCES 
The dark shales, less than 10 feet thick near the deep pit, thicken very 
rapidly toward the north and, as shown in the photograph, form the notable 
feature along the central line of the trench. They contain thin bands of 
whitish sandy rock which contrast sharply with the other beds and serve, 
by converging toward the coal exposure, to show that the rapid southward 
thinning of the mass is not due to a scpieeze, but that the conditions are 
similar to those seen in FEsperance. At about 100 feet from the deep pit 
and on the platform at the right side of the photograph, a trial pit has been 
sunk, reaching the Banc inferieur, which is shown to the thickness of six 
or seven feet. The dip is 40 degrees and the coal is cut off sharply; on this 
leveled edge, the dark shales rest, dipping at 55 degrees in the same direction, 
but they are apparently conformable to the Banc des Brouillages in the 
easterly wall. 
The explanation of these relations, as of those in FEsperance, would be 
sought for at once in a thrust. But in that case the Banc des Brouillages 
should be involved, the part of that division above the plane of non-conform¬ 
ity should rest on higher portions of the Grande Couche and one would be 
justified in expecting to find at least some traces of those higher portions in 
other exposures, between the Brouillages and the dark shales. But the 
miners know of no coal underlying the Brouillages at this place; that part 
of the Grande Couche is well shown at few yards away, several feet beloAv 
the bottom of the trial pit and at least 12 feet below the plane of non-con¬ 
formity in that pit; thence it is absolutely continuous up the easterly wall 
to the top of the trench. At barely 10 yards away in the opposite direction 
and at less than 20 feet above the top of the trial pit, the dark shales and the 
Brouillages are in contact and they are conformable. It is certain that the 
agent which carried away the Banc inferieur and higher portions here did 
not affect the Brouillages to any appreciable extent. 
A long extension of the trench begins at somewhat more than 20 feet 
above the level platform shown in the photograph and continues toward 
FEsperance. Along the easterly side, the dark shales having crossed the 
higher portions of the Grande Couche, they rest conformably against the 
steeply dipping Brouillages or lower part of the Grande Couche, which 
forms the easterly wall. Following this extension, one at length finds the 
upper portions of the coal bed in the floor and at the end, at the foot of the 
northerly wall, an exposure shows the coal again cut off abruptly, with the 
dark shales resting uheonformably upon its edge. The shales above the 
plane of fault are the dark shales and the illustration shows their flaggy 
structure; the shales conformable to the coal, below the plane show very 
little tendency to that structure and are evidently of different type. The 
conditions are exhibited in Plate XX, figure 1. 
