April, 1911.] The Ancient Vegetation of Ohio. 323 



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 CO2 existed in much larger quantities 

 than tiow, since enonnous amounts have been fixed in the beds of 

 limestone. The depletion of the COo 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 ihe 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 



