32 2 The Ohio Naturalist. [Vol. XI, No. 6, 



spernis related to the modern conifers and flowering plants of 

 which indeed they nia}^ have been the ancestors. Of these the 

 best known are Cordaites, Megalopteris, Alethopteris and possibly 

 Lyginopteris with its spiny stem and highly dissected xerophilous 

 foliage, Bennettites, and perhaps Ginkgo. All these were strik- 

 ingly cosmojiolitan in distribution, extending to high latitudes. 

 They were at their climax of vigor and height, and verged into 

 more recent types. 



How the coal fields were formed hundreds of centuries ago 

 may be seen at any of our lakes today. Our lakes and ponds 

 represent only one of the several conditions under which vege- 

 table matter accumulates. Other but less important ways possi- 

 ble to form coal beds are accumulations (1) built up from the 

 ground by successive elevations of the water table; (2) in sea 

 bottoms beneath "sargasso" vegetation; and (3) in marine 

 swamps including mangrove swamps and coastal salt luarshes. 

 The slight admixture of sediment which indicates the absence of 

 waves, tidal currents, wind-formed currents and eroding rivers, 

 and the fact that at present only one kind of tree, the mangrove, 

 grows in salt-water, is against the view that the coal was 

 fomied in salt-water. No records exist to show that in earlier 

 ages the vegetation of the ocean differed greatly in kind from that 

 now predominating. Ferns and mosses are entirely absent from 

 the ocean; the main marine vegetation is still formed by algae, 

 often highly differentiated, which belong to diverse orders. The 

 manner in which the bed of vegetable matter accumulated, and 

 how it was kept from decay, is a long and interesting chapter. 

 The process has been described elsewhere (10) in more detail. 



Critical periods suddenly arrived, possibly subsidence accom- 

 panied with a deluge of water from an adjacent sea, lake or 

 aggrading stream, carrying silt, l^urying the vegetation under 

 deposits of mud and sand and converting the submerged portion 

 into dry land. The rise in water level brought with it the recur- 

 rence of swamp conditions, but the succeeding shallow lake had a 

 narrower area than its predecessor, and around its shores and in 

 island-like masses flourished again a dense luxuriant vegetation. 

 In long-continued growth it existed, filling the lake with an accu- 

 mulation of vegetable debris to the depth and the margin which it 

 still retains as the present coal field. During its formation the 

 nature of the sub-soil on which the vegetation grew, and the 

 drainage relations affected then as now the character of the plants 

 predominating in an area, and thus influenced the percentage and 

 kind of ash in the vegetable debris. Frequent local or general 

 disturbances in topography and sedimentation during times of 

 flood brought about the occurrence of partings and seams in coal 

 beds. Not infrequently the vegetation was buried under sheets 

 of limestone that accumulated through precipitation in the invad- 



