104 ILLINOIS ACADEMY OF SCIENCE 
during the accumulation of the vegetable matter of each of 
the large coal beds. It assumes such a depth of water above 
the accumulating vegetable matter that the charred fragments 
brought in by the streams could be freely floated out above 
the mass of vegetable matter already present, to every part of 
the basin; and most impossible of all, that the streams that 
carried such vast quantities of charred vegetable matter car- 
ried at the same time little or no mud or mineral sediments. 
If it is assumed that the water of the basin was so shallow that 
the clay and sand brought down by the streams were strained 
out in the meshes of the tangled plant debris near the margin 
of the swamp, then the same vegetable sieve would catch the 
charred fragments and not permit them to be distributed to 
every part of the basin in which the vegetable matter was ac- 
accumulating. It will be seen that this explanation is not at 
all in harmony with the facts of the vertical and horizontal dis- 
tribution of the mineral charcoal bands in the coal beds. 
A modification of this view assumes that the mineral char- 
coal represents partially burned vegetable matter resulting 
from fires sweeping over the surface of the marshes in which 
the vegetable matter of the coal beds was accumulating. It is 
not probable that fires would start from lightning and travel 
over water-Covered swamps with only the living undergrowth 
and green leaves and branches of the trees to support the 
flames; and if they did they would not leave such a uniform 
and thick layer of charred fragments as would be required to 
form the mineral charcoal that occurs in the well developed dull 
laminae. If it is assumed that the surface of the vegetable 
matter that had accumulated in the swamp had been exposed 
to the atmosphere and partially dried before the fires swept 
over it; then the general conditions involved would be similar 
to those under which the mineral charcoal is interpreted as hav- 
ing been formed by the partial atmospheric decay of the upper 
surface of the vegetable material of the bog exposed during 
periods of unusual low water, without the action of fires. 
It seems to the writer that the explanation of mineral char- 
coal as resulting from the temporary exposure and partial 
atmospheric decay at the surface of the vegetable matter in 
the bog, instead of the assumption that it must have been 
charred by fire, is much more consistent with the following 
facts: (1) the frequent repetitions of the dull laminae con- 
taining such considerable thicknesses of mineral charcoal; (2) 
the larger number of plant spores in the dull laminae than in 
the bright coal; (3) the numerous pinnae and pinnules of 
