24 ROYAL SOCIETY OF CANADA 
The stages in which variations in the hydrogen percentage and other 
chemical differences may be expected can be discussed under the three 
following heads:— 
(1). Variations in the original composition. 
(2). Duration and character of decay. 
(3). Amount and kind of alteration due to dynamic and geo- 
logic influences. 
VARIATIONS IN ORIGINAL COMPOSITION. 
The plants which made up the deposits now found in the coal 
measures of the Carboniferous are of early types and we can judge of 
their composition only by referring to those of somewhat similar forms 
which belong to the existing flora. There is a possibility that in the 
old forms the composition has been preserved more or less in the simpler 
ones of the present; but as there is found no great range in composition 
among these, it is inferred that the composition of the old plants 
had no very wide range. The early types have given rise to many 
varieties so that in plants of later times there is a much larger 
variation in chemical composition. The plants which are supposed to 
contribute largely to these coal deposits even in later times are the 
smaller varieties in which variations from the average woody fibre are 
small. We may therefore conclude that in original composition the 
plants have had no very great influence on the final composition of the 
coal; but that physical characters which indicate different rates of decay 
are of more importance. 
It is quite noticeable in plants that the herbaceous parts are more 
susceptible to decomposition and disintegration than the stems and 
harder parts. Differences in chemical composition in the several parts 
of the plant are also noticeable in that the leaves and twigs contain 
higher hydrogen percentages than the wood and bark. 
This seems to indicate that the herbaceous plants would be high in 
hydrogen compared with varieties having woody tissue as a principal 
component, so that there is a possibility that the smaller plants might 
form deposits which would originally differ in composition from other 
masses. Where however vegetation was of a mixed character although 
there may have been original differences in composition of the different 
plants, they were so mingled together in the mass that they do not affect 
the coal except in appearance. The soft vegetation by its easy disinte- 
gration loses its organic structure and assumes the appearance of a jelly- 
like mass which probably constitutes the material which in many cases 
forms the bright coals or the bright streaks in dull varieties, such as the 
Lower Cretaceous coals of the Rocky Mountains. The partly obliterated 
