320 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 ami 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 w4th ferns. 

 The vegetation must have moved into the open water of pro- 

 tected bays and inland water basics 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 mxust 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 fomiing 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 nonnal 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-organi.sms (22) have given their 



