STEVENSON, COAL BASIN OF COMMENTRY 
175 
along the southerly wall, he reaches the dull dark shales, already referred 
to as resting unconformably on the Grande Couche. They dip at 25 degrees, 
but whether or not they are conformable to the gray sandstone here could 
not be determined satisfactorily, as the bottom of that deposit seems to be 
very irregular. 
The condition is perplexing. These shales bear no resemblance in 
color or texture to those underlying the Gres Noirs on the long westerly wall; 
there is no evidence along that wall that any disturbance took place just 
prior to the deposit or during the deposit of the gray sandstone, for the little 
coal rider of the Grande Couche is continuous under the sandstone. Yet 
just east from that wall, the Grande Couche and its overlying gray shale 
have been cut off and the dark shales, which clearly underlie the Gres Noirs, 
rest on the edge of the coal with different rate of dip, though in the same 
direction. 
In the southerly wall, these dark shales, where first seen, have a dip of 
25 degrees; within a few feet, they rest unconformably on similar shales 
with at first 15, then 20 degrees dip — the relations are shown in Plate XVII, 
figure 2. These seem to suggest a thrust; one is here at several feet about 
above the unconformity shown in Plate XVI, figure 2, which is distant only a 
few yards and the inclination of the planes is not the same. 
Just here, however, one finds an abrupt change in the southerly wall. 
The dark shales suddenly become crumpled for a space 10 or 12 feet 
wide at the top of the wall but tapering downward so as to be insignificant 
within 20 feet; at once they are succeeded by a wholly different rock, oc¬ 
cupying a trough in the shales. This is the phenomenon termed by Fayol, 
the Glissement de l’Esperance, and the features appear in Plate XVIII, 
figure 1. The space of plicated shale is not included. The easterly side 
of the trough is covered with vegetation and debris so that it could not be 
determined whether or not the Banc des Brouillages is involved. The dark 
shales underneath this rock-filled trough are partly covered by debris from 
the soft rocks above; but enough was seen to make clear that they are not 
crumpled. Coal seems to be in place at the foot of the wall, but its relations 
to the shales, two feet above, could not be ascertained; nor could the appar¬ 
ent thrust shown in Plate XVII, figure 2, be traced with certainty underneath 
the trough. 
The material filling this trough bears no resemblance to anything seen 
elsewhere within the area of les Pegauds. It consists largely of light colored 
more or less feldspathic sandstone, with some light colored shales along with 
some bituminous shale and a large fragment of coal. All of the beds are 
closely folded and the coal fragment, as shown in the photograph, is crumpled 
into a double-ended hook. 
