FUCOIDES IN THE COAL FORMATIONS. 327 



cations that remains of marine plants might have existed at some places mixed with the 

 aerial plants of the bogs of the coal epoch, it was not easy to account for such a phenom- 

 enon as that of the formation of coal and petroleum at the same horizon and under the 

 same circumstances. But this curious fact, I think, is explicable now. When the com- 

 bustible matter has been formed especially from the remains of aerial plants, whose tissue 

 was mostly vascular, or vascular and cellular, like that of the Lepidodendran, Sigtllaria, 

 ferns, etc., it becomes by mineralization a hard coal, with thin layers or distinct laminas, 

 sometimes shining, sometimes mixed with opaque layers and flakes of charcoal, and giving, 

 by combustion, a proportion of ashes according to the nature of the wood. When it has 

 been formed merely by floating fresh-water vegetables, like Stigmaria and its leaves, the 

 compound, originally half fluid and more easily decomposed, becomes, by the slow process 

 of combustion, compact, homogeneous, without apparent layers, tending to mere bitumen, 

 thus forming the different varieties of cannel coal. Now, I believe that when this floating 

 vegetation has been more or less densely intermixed with marine plants, and perhaps also 

 influenced by marine water, the almost total absence of woody fibres has casually prevented 

 the bedding of the material, and so, by slow maceration, part of it has been transformed 

 into fluid bitumen. It is probably for this reason that we see, sometimes, as at Brecken- 

 ridge, in Kentucky, a bed of cannel coal so nearly decomposed into petroleum that it can 

 scarcely be used as coal, and at a lower level, even in close proximity, and where every 

 trace of coal has disappeared, inferior strata of sandstone, strongly impregnated with 

 petroleum. 



In descending from the base of the Coal Measures into the Devonian, we find deposits 

 of oil nearly in the whole thickness of this formation, with the exception of the old red 

 sandstone, equivalent of the Ponent and part of the Vespertine of Pennsylvania. All the 

 plants of this formation, and they are numerous enough, belong to swamp or land plants, 

 and no trace of petroleum has been seen in these measures. But down from this red 

 sandstone, the Chemung is full of remains of Fucoides, and where they are found all the 

 sandstone strata of this formation are more or less impregnated with oil. 



Still lower the black shales of the Hamilton group are so much charged with bitumen 

 that they have often been considered as the true source of the Devonian petroleum. There 

 the remains are nearly, almost totally, obliterated. A few teeth of fishes and small shells, 

 very rarely large trunks of Lepidodendtwi, nothing more, at least in those extensive de- 

 posits, generally of great thickness, which border our Western coal basins. The color of 

 these shales, and the bitumen which they contain, indicate a formation under water, under 

 the influence of a powerful vegetation ; and a marine vegetation, without doubt ; else, 

 besides the well-preserved trunks of Lepidodendron, which have probably been brought 

 floating, we should find there other remains of aerial plants. At Worthington, in Ohio, 



