STEVENSON, COAL BASIN OF COMM ENTRY 
183 
This lowest sandstone is shown on the northerly wall near the head of the 
trench where it is 17 feet thick. But as one advances into the trench, he 
finds the Brouillages structure prevailing on the northerly wall. 
The complexity of deposits shown in the long almost sheer wall of these 
trenches far exceeds anything observed in the other trenches and is intima¬ 
tion that one is approaching the massive delta of the Montassiege area. 
Here one sees in full detail all the changes which geologists elsewhere, 
depending on separated sections and records of borings, have expressed in 
diagrams but which they have never seen in place. 
About half way in this trench, the yellow sandstone is separated by per¬ 
haps 70 feet of shale and sandstone from the highest coal-bearing shale 
below; but at about 300 feet farther the interval is barely half as much. 
Almost midway between these points, a group of beds, estimated at 40 feet, 
is folded, curled on itself and cut off abruptly, but the overlying beds are 
undisturbed. The sandstone at the bottom of the wall seems to be that 
observed in the Grande and Saint-Edmond trenches. Ordinarily it is 
regularly bedded, but occasionally it is cut out by downward extension of 
the overlying shales. At many places it swells below and cuts out the under¬ 
lying shales. These projections below have no definite bedding and bear 
little resemblance to the main bed. They are often gnarled like burly wood; 
at times they consist of thick rudely concentric bands; while at others they 
are made up of folded layers. Here one can see all variations of the coal 
measure sandstones, in full day, showing the features of delta deposit as 
American geologists have conceived them. 
The coal has been removed for a long distance and the almost con¬ 
tinuous “fall” prevents study on the southeasterly side; but on the opposite 
side of the trench one finds along the great face a succession of coal, coaly 
shale and sandstone, recalling in some respects the Gres Noirs conditions of 
Longeroux but for the most part those of the Banc des Brouillages in the 
eastern trenches. The coal is more or less slaty, but in one layer, mined 
apparently for local use, it is very clean. 
The shales associated with the coal afford ample evidence that they 
have endured severe pressure, such as accompanies distortion. All are at 
times much contorted, are flaky and polished as though they had been the 
soft material between harder beds, and had yielded so as to become pockety. 
The conditions are not unlike those observed in the Poeono coal beds within 
the faulted folds of southwestern Virginia. 
Variations of the Grande Couche. 
It remains now to describe the variations of the Grande Couche at the 
extremities of the outcrop as well as in the deeper parts of the workings 
