190 
ANNALS NEW YORK ACADEMY OF SCIENCES 
Origin of the Grande Couche. 
Fayol’s thesis respecting the origin of coal beds is this: 
The beds of coal were formed after the same manner as the beds of shale and 
sandstone; the plant materials carried by the streams along with clay, sand and 
pebbles, w T ere mingled sometimes in midst of the mineral sediments, sometimes 
heaped in beds or masses more or less pure. Just as the clay, carried simultaneously 
with the coarser elements, is fixed partly in midst of those elements and at the 
same time forms some distinct beds. In like manner, plant debris, which, from the 
standpoint of sedimentation, is equivalent to fine mineral particles, remains partly 
in midst of the coarser sediments and is deposited especially along with the clay or 
in its vicinity . 1 
Fayol presents a careful calculation aiming to show that the drainage 
area of the lake was sufficient not only to supply all vegetable matter needed 
to form the bed, but also to supply it in a very short time. He estimates that 
to complete the Lower measures, a period of 13,000 years may have been 
necessary, as the streams were small and the advance of the deltas very slow; 
but with lengthening of the streams the advance was more rapid, so that 
deposition of the Middle and Upper measures required only 4,000 years. 
One hundred seventy centuries sufficed for accumulation of the whole 
deposit, including the coal beds. 
The surface for vegetation was eo-extensive with the drainage area. 
At the beginning, this was confined to some hectares of abrupt shore, as the 
mountains rose to perhaps 1,000 meters above tide [or about 1,200 feet above 
the lake surface]; but when the Grande Couche began to form, the emerged 
surface of the deltas had an area of 1,800 hectares [about seven square miles] 
and the streams gathered water from 10,000 hectares [barely 40 square miles]. 
At the end of deposition, the alluvial plain was 3,100 hectares [about 12 
square miles] and the whole drainage area was 16,000 hectares [nearly 63 
square miles]. On the average, the available area for vegetation during 
the earlier period was about 2,000 hectares and for the later about 15,000 
hectares. 
The amount of coal from a Cordaites stem has been determined. Reason¬ 
ing from this, Fayol shows that a forest of Cordaites trees, each individual 
having a space of 10 meters square and attaining full growth in 50 years, 
would yield during each century a layer of coal, 60 millimeters thick over 
the whole area. In addition, the herbaceous plants and shrubs, such as 
ferns, lepidodendra, calamodendra, forming the underbrush, would furnish 
as much coal as the trees per unit of surface. But the amount of coal in the 
1 Commentry, p. 17. 
