SEVENTH ANNUAL MEETING 109 
shallow swamps, and the consequent exposure of successive 
levels of the vegetable matter to the air, is the only adequate ex- 
planation that accounts for the extensive bedding- planes prac- 
tically free from clay sediments, the general distribution and 
alternation of the bright and dull laminae and the large amount 
of mineral charcoal in the latter, as they occur in the coal beds 
of Illinois. According to this View the bright laminae result- 
ed from the imperfect putrefaction of the vegetable matter en- 
tirely under water, while the dull laminae and mineral char- 
coal resulted from the partial atmospheric decay previous to 
the more complete subaqueous putrefaction. 
If the above view is correct, the dull laminae and mineral 
charcoal partings of the coal beds are the records of repeated 
interruptions of accumulation of the less woody kinds of plant 
material, during which the surface of the vegetable mass in the 
swamp was above water and exposed to partial atmospheric 
decay which resulted in the destruction of the softer parts of 
the plant tissues, leaVing them in an indurated and more or 
less skeletonized and fibrous condition. On resubmergence 
these residual portions of the vegetable materials were not so 
readily impregnated with the fundamental matter of the bog 
as were those parts of the mass that had not suffered partial at- 
mospheric decay, and hence in the process of bituminization 
these bands of harder, more skeletonized and so more fibrous 
vegetable matter became transformed into mineral charcoal. 
Such periods of arrested growth and accumulation of the 
more herbaceous and succulent kinds of aquatic plants, due 
to the exposure of the surface of the vegetable matter of the 
bog, would be favorable for the accumulation on such a sur- 
face of a relatively larger proportion of spores than would be 
mingled with the vegetable mass during periods of submer- 
gence and of normal vegetable growth in the bog. The re- 
sistant nature of the spore cases would also permit their better 
preservation than the ordinary plant tissues during such times 
of exposure. These conditions would explain the greater 
abundance of spores in the dull than in the bright laminae of 
the coal beds. The variation in thickness of the dull laminae 
is assumed to be due to the unevenness of the surface of the 
exposed matter in the bog. The relatively smaller percentage 
of volatile matter, and larger percentage of fixed carbon in the 
mineral charcoal and dull laminae, would be explained in part 
by the fact that during the times when the surface of the veget- 
able mass was above water and exposed to atmospheric decay, 
the volatile products of decomposition escaped into the air. and 
probably in part because the material of the dull laminae were 
