3 22 
The Ohio Naturalist. 
[Vol.XI, No. 6, 
sperms related to the modern conifers and flowering plants of 
which indeed they may have been the ancestors. Of these the 
best known are Cordaites, Megalopteris, Alethopteris and possibly 
Lvginopteris with its spiny stem and highly dissected xerophilous 
foliage, Bennettites, and perhaps Ginkgo. All these were strik- 
ingly cosmopolitan 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 marshes. 
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 
formed 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, burying 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- 
