STEVENSON, COAL BASIN OF COM MEN TRY 
195 
been followed to their disappearance. On the east side, the more peaceful 
Colombier rarely broke across the plain, and the marsh followed with little 
interruption the slowly extending strand southward. The struggle between 
swamp and petty streams along the northern border was seen in l’Esperance, 
where, within little more than 600 feet, the great coal mass is broken into 
thin beds of carbonaceous shale separated by coarse material. 
The area in which this accumulation was made embraces not far from 
1,000 acres. The abundance of mineral charcoal (fusain) shows that the 
surface of the swamp had frequently only a thin covering of water and that, 
at times, parts of it were bare; cannel and c-annel shale mark the presence 
of pools into which fine silt and vegetable mud were carried; while the 
constant irregularity and impurity of the Banc superieur make clear that 
toward the close the bog was exposed to overflows of very muddy water, 
which at length became so frequent as to destroy the vegetable growth. 
The Banc des Chavais is an ordinary phenomenon, not unlike the “sand¬ 
stone faults” of other regions. An outlet of the Colombier had pushed its 
way across the swamp. Shallow at first, it carried only fine silt; during a 
flood or during temporary obstruction of the main stream, it deepened its 
channel and for a time it may have been the chief outlet, carrying down the 
coarse material to be mingled with portions of the swamp itself. But it 
aggraded its lower reaches through the bog; becoming shallow, it carried 
only fine silt and at length was obliterated by the swamp growth. Irregu¬ 
larities in partings indicate lines of petty streamlets following temporary 
channels. 
There is said to be nothing resembling an ancient 1 soil of vegetation and 
this is taken to be evidence against the hypothesis of origin from plants in 
situ. No information is given as to what are the necessary characteristics 
of such a soil, but it can be said positively that underclays with Stigmaria 
are wholly wanting. Stigmaria occurs only in the roof shales of the Grande 
Couche on the west side of les Pegauds, where it is associated with Lepido- 
dendron ; neither genus has been found on the east side. Sigillaria is un¬ 
known, save by a single cicatrix discovered in the Lower measures. 2 The 
absence of these forms does not concern the matters at issue; it shows only 
that the coal was formed from other plants, such as have contributed to coal¬ 
making elsewhere as well as here. A bed of impalpable clay is not necessary 
for the formation of a swamp; the sandy clay underlying the Grande Couche 
is crowded with vegetable remains and it is clayey enough to prevent down¬ 
ward drainage. 
1 Fayol: Commentry, p. 239. 
2 Fayol: Commentry, p. 239, 132. 
