166 
ANNALS NEW YORK ACADEMY OF SCIENCES 
beds of shale, in all about 30 feet, 1 begins at a few feet above the coal. The 
lower half of this mass disappears within 100 feet. There is no replacement, 
but simple thinning and the underlying shale is brought into contact with 
the upper part of the sandstone. As the lower portion approaches the place 
of disappearance, it becomes irregular and, on the weathered surface, 
resembles a contorted schist. This thinning is in the direction of the strike, 
and there seems to be no variation in the dip. The change is wholly in the 
sandstone, as though the shale surface were inclined when the upper beds 
were deposited almost horizontally. Owing to this thinning, the upper beds 
are brought nearer to the Grande Couehe. Similar variations appear fre¬ 
quently on this wall and they have been emphasized properly by Fayol as 
evidence of delta deposit. They have been accepted as such proof by 
American geologists for at least half a century. 
The upper portion of the sandstone persists to the east end of the trench 
where the floor rises to its level. It is light gray, has much feldspar, is 
moderately coarse grained with occasional pebbles and contains abundance 
of stems and leaves, whose position bears no definite relation to the plane 
of bedding. It holds also many lentils of coal, from mere films to one which 
is four feet long with greatest thickness of 10 inches. A sandstone, on the 
northerly wall and at only a few feet below the coal bed, is coarse, with 
pebbles as large as a pea, but not numerous enough to make the rock a con¬ 
glomerate. 
The Grande Couehe is shown imperfectly at the east end of the trench, 
where one sees the tunnel in the coal, leading to the next trench beyond. 
The coal is almost 30 feet thick here and, according to Fayol, 2 the thickness 
in this trench varies from 10 to 12 meters. The exposure of the lower por¬ 
tion suffices to show the presence of irregular plates of rock. A dike of 
igneous rock, termed dioritine or micaceous prophyry by Fayol, appears at 
this end, but the exposure is so incomplete that nothing can be ascertained 
respecting its extent. Where that rock cuts through the Grande Couehe on 
the south wall, the coal laminae are bent upward at nearly right angles and 
the metamorphism seems to be complete. The luster is graphitic at two 
feet from the contact, but at five feet the change is barely perceptible to the 
eye. Fayol states that for nearly 200 meters along the strike, the coal is so 
altered that it can be ignited only with difficulty. A rock of similar type is 
shown near the bottom of the coal bed on the opposite wall. 
1 The thicknesses given for rocks in the walls are all estimates, as direct measurements 
cannot be made. 
2 Commentry, p. 263. 
