176 
ANNALS NEW YORK ACADEMY OF SCIENCES 
Tranchee de Longeroux. 
Leaving the Tranchee de l’Esperance by the stairway at this end, one 
passes over the whole of the Gres Noirs group and, following the alluvial 
cover, reaches the even more imposing Tranchee de Longeroux within a 
few rods. There the exposures are almost complete and reveal conditions 
much more complicated than those of l’Esperance. The yellow sandstone 
is at the top of the wall as one enters the trench and at 65 feet lower on the 
westerly side are two openings in the black shale. Half-way down to the 
latter and on the first bench, one is at the western border of the Glissement 
de l’Esperance, where the trough certainly seems to extend upwards into 
the yellow sandstone, but the contact is not shown. At the end of this 
platform, one reaches the basal sandstone of the Gres Noirs, which is divided 
by the stairway. There the sandstone has been pushed into a recumbent 
fold involving also the black shales, which are well exposed alongside in 
the wall. The photographs here are unfortunately on the same film, as the 
writer neglected to bring a fresh film into place. But the fold in the shales 
is recognizable in Plate XVIII, figure 2, being on the right side of the picture; 
its place is at the left above the stairway. The fold in the sandstone is 
obscured in the photograph. 
At a few steps from the spot where this view was obtained, the contact 
between the gray sandstone and the dark shales is shown and they appear to 
be conformable. The shales are dark gray to lead-gray, fine-grained, tend 
to be flaggy and contain many excellent impressions of plants. They are 
sharply folded and the surfaces of the flaggy layers are often slickensided. 
The black shales of the Gres Noirs very frequently exhibit similar slicken- 
siding. The polishing in both shales is such as one could expect to find in 
materials already hard. At times it is as marked as that observed in Ordo¬ 
vician shales within the Cumberland valley of Pennsylvania. 
At a short distance from this exposure there are two openings in the 
black shales, which contain so much coal that, at 50 feet away, they resemble 
a bed of solid coal. The yellow sandstone is shown at top of the wall in an 
exposure, about 150 feet long, where it rests with irregular base on the 
black shales; it is cross-bedded but in thick layers, not in laminae. Plate 
XIX, figure 1, shows that this crossbedding is not shared by the under¬ 
lying shales. Whether or not the structure is original or secondary could 
not be determined; the underlying shales are much folded. Just beyond 
the opening at the left of the picture, a wedge of sandstone begins which 
increases to the end of the trench, where it is 12 feet thick; it is light gray 
and bears close resemblance to the basal sandstone of the group. 
