April, 1911.] 
The Ancient Vegetation of Ohio. 
3 2 3 
ing water. In the subsequent submergence and fossilization there 
followed other marshes and bog-like swamps. These coal beds 
represent in some places submerged forests, and in others the 
coal was probably formed not by the slow growth of vegetation 
in situ, but from drifted vegetable material. But every successive 
coal forming area had a narrower lowland basin than its pred- 
ecessor. This indicates that the changes in the relative level of 
water were not accompanied by oscillations in land level. 
The geological evidences of the earlier periods of the state’s 
development show that C0 2 existed in much larger quantities 
than now, since enormous amounts have been fixed in the beds of 
limestone. The depletion of the C0 2 content, it may be pre- 
sumed, produced effects on the atmospheric blanket which tended 
to lower the average temperature and moisture and this changed 
the climatic character of the region (5). Similarly the tremen- 
dous amounts of carbon stored in the -basins of the coal measures 
by the work of green plants undoubtedly produced a marked 
effect on the atmospheric content of carbon dioxide. Far reach- 
ing changes in climate must have followed, such as are exemplified 
in the periodic glaciations of the Pleistocene. 
The duration of the Carboniferous period must have been a 
very long one to yield deposits of coal of such thickness, for it 
should be remembered that a large part of the vegetable matter, 
about four-fifths, escaped as gas in the making of coal, and the 
remainder has been compressed to a fraction of the original layer 
of vegetable debris. It is estimated that from 15 to 30 feet of 
peat are required to make one foot of coal. By a series of changes 
which are plainly traceable, vegetable matter, peat, lignite, 
bituminous or soft coal, and anthracite form a series of substances 
which grade one into another in an unbroken line from complex 
organic partly oxidized compounds at one end to nearly pure 
carbon at the other. The succession is not necessarily a strictly 
lineal one, since degree of decomposition and chemical changes, 
previous exposure of the vegetation to reduction action or to 
oxidation, affect the alterations in various ways. The meta- 
morphic changes are hastened where the structural condition 
of the overlying rock favors the escape of the gaseous products. 
Ligno-cellulose compounds are the initial substances which grad- 
ually loose carbon dioxide, marsh gas and water, and so yield the 
series of products represented by the different kinds of coal. 
Chemical analysis (3) in which the probable combination of ele- 
ments is given grouped as moisture, volatile hydrocarbons, fixed 
carbon, ash and sulphur show that the value of coal for fuel is 
determined mainly by the relative amounts of its volatile hydro- 
carbons and the fixed carbons. The former represents the free 
burning constituents of coal and the latter its heating power. 
Ash and sulphur illustrate the objectionable impurities. Up to a 
