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ANNALS NEW YORK ACADEMY OF SCIENCES 
erosion. Pebbles of this kind are not confined to rocks above the Grande 
Couche or to the area of les Pegauds. Fayol states that they occur in the 
lower division of the coal measures as well as in the higher division within 
both les Pegauds and les Ferrieres. In an interesting comparison, he shows 
that the coal of the pebbles resembles that of the vicinity. Those near the 
anthracite of the lower division are anthracite; those near the Grande 
Couche are of fat coal, though, as should be expected, an occasional pebble 
of anthracite appears among them; while in the area of les Ferrieres they 
are feebly coking as is the coal of the main bed in that area. 1 
Tranchee des Chavais. 
At a few rods beyond ForG is the abandoned trench of the Chavais, in 
which the two partings of the Grande Couche — Banc des Chavais and 
Banc des Roseaux — were found in fine development. But this trench has 
been abandoned for many years; it is filled in great part and vegetation 
covers much of the decayed wall, so that little of interest remains exposed. 
A walk of two minutes brings one to the Tranchee de l’Esperance. 
Tranchee de l’Esperance. 
The enormous excavation which is known as the Tranchee de l’Esper- 
ance is on the eastern prong of the outcrop. Mining operations continue 
here and the exposures on all sides are still nearly complete. The pit is 
almost 100 feet deep, not less than 500 feet long and, in places, fully 200 
feet wide at the bottom. Nearly all of the curious features described by 
Fayol twenty years ago are distinct to-day, while advance in the work has 
brought others into sight, which serve in some cases to make the conditions 
clearer but in others only more perplexing. 
Entering the trench at the northerly end, one finds at 70 feet, by barom¬ 
eter, above the Grande Couche, a thin streak of coal underlying the soft 
basal sandstone of the Gres Noirs. Below this are gray shales with thin 
streaks of soft whitish sandstone or very sandy shale. One bed has many 
pebbles and fragments of sandstone, and around the latter the structure of 
the shale is as though it had been deposited in an eddy. Here and there 
one sees fragments of dark shale, and pebbles of coal are not rare. 
It is deserving of note that none of the coal pebbles found by the writer 
showed any signs of contraction after burial; all the pebbles, coal and shale 
alike, were so securely fastened that removal without fracture was difficult. 
1 Commentry, p. 141. 
