AGE CHARACTERISTICS OF COALS 
139 
GEOLOGICAL AGE CHARACTERISTICS OF THE COALS 
By John J. Stkve^nson 
Since the extent of chemical change of rocks increases as a 
rule proportionally to the antiquity of the deposits the tenor of 
the fossil fuels is advantageously considered in the order of their 
occurrence in geoloigical time. A summary account of the accumu¬ 
lation of coal in beds is presented ^ in a recent treatise on the 
“Formation of Coal Beds.” Other phases are included in an essay 
on the Interrelations of the Fossil Fuels.^ Closely related problems 
have to do with the ascertainment of the relations of the fossil 
fuels, other than petroleum, in their physical and chemical re¬ 
semblances and differences. 
Peat is the familiar accumulation of more or less changed 
vegetable matter observed in localities sufficiently moist. It is most 
abundant in Pleistocene and Recent deposits, but a very similar 
material occurs in Tertic formations, and even in the Carbonic 
terranes one often finds a substance which in hand specimens can 
hardly be distinguished from well-dried peat. 
The area of Quaternaric and Recent peat deposits is apparently 
greater than on which carbon deposits were laid down during 
any preceding period of similar duration; yet it is but a small part 
of the earth’s surface, for there are vast spaces on which no peat 
has formed since the Quaternaric period began though much of 
the peatless regions has been forested. 
Peat bogs vary in size from a few square feet to thousands of 
square miles. The smaller deposits are due to filling of pools, 
ponds and lakes by plant invasion; while the more extensive 
deposits, those on coastal, or broad river, plains originated, certainly 
in some, probably in most, cases in small, isolated bogs, which 
became united by transgression. These, though continuous super¬ 
ficially, are not strikingly contemporaneous throughout. The buried 
1 Proc. American Philos. Soc., Vol. ly, pp. 1-116, 1911. 
2 Ibid., Vol. I,V, etc., 1921. 
