3 20 
The Ohio Naturalist. 
[Vol. XI, No. 6, 
measures or ancient vegetation deposits. In the northwestern 
corner of the state the strata dip northwest from the anticlinal 
axis and pass under the Michigan coal basin, precisely as the same 
series east of the anticlinal dip beneath the Allegheny coal field, 
of which Ohio’s coal area forms a part. 
The well-marked order of arrangement which the coal fields 
of Ohio present, suggests that at the beginning of the Carbonifer- 
ous age an arm of an ancient shallow lake extended inland and 
continued in an unbroken sheet up to the Cincinnati arch which 
made its western boundary. Year after year for many centuries 
an exceedingly dense luxuriant growth of vegetation covered the 
surface of the shallow basins as scattered swamps and bog-like 
marshes sometimes running into a long connected chain, and 
sometimes quite isolated. The vegetation was doubtless of many 
kinds of trees, especially giant ferns and club-mosses, with an 
undergrowth of shrubs, and plants like grasses and sedges. There 
were many minor differences between the vegetation of different 
basins; zones of predominating lycopods alternated with ferns. 
The vegetation must have moved into the open water of pro- 
tected bays and inland water basins progressively, as groups, 
distinct in physiognomy and growth-form, the zones varying in 
width with the definite conditions of life and the selective action 
of the habitat. The plankton formation must have been followed 
by plants nearer the margin and submerged along the gently 
sloping shore lines. Free floating forms similar to Azolla, Salvinia, 
and to various algae must have existed in great masses, easily 
transported by winds and currents, at times completely covering 
the quiet pools. As their debris formed a slowly rising deposit in 
the basin, the littoral or shore formation must have advanced 
toward the center of the water basin forming a mat of interwoven 
rhizomes and roots, harboring various societies and layers accord- 
ing to the light and water conditions. In time the basin became 
filled with the debris of the vegetation. In many cases the vege- 
tation accumulated to a depth of more than fifty feet, but this 
great distance from the mineral substratum or the deficiency of 
mineral substances never rendered it difficult or impossible for 
the plants to grow luxuriantly. Green plants utilize water and 
the carbon dioxide of the air to form food, the starches, sugar 
fats, and proteins necessary to their nourishment and for the 
successive phases of a normal development. The mineral soil- 
constituents are not the food of plants; they are indispensable but 
their amount is very small in organic substances, and alone they 
are incapable of sustaining life in plants. 
Trees standing erect within a bed of coal, their horizontal roots 
still embedded in the underlying stratum; the corky bark, the 
wood, branches, leaves, spores, and fruits of many plants, and 
even the remains of fosil micro-organisms (22) have given their 
