194 PAPERS RELATING TO NATURAL, HISTORY. 



size and the prodigious fatness of their bodies. The green fat of the turtles, 

 says Harvey,t so much prized by aldermanic palates, may possibly be colored 

 by the unctuous green juice of the Oaulerpae, on which they browse. The same 

 eould be said of the color of the Devonian petroleum, which is exactly that of 

 the Chlorosperm Hydrophytes. It is not positively ascertained, I believe, if 

 whales and other marine mammifers of this kind, whose bodies are large reser- 

 voirs of oily matter, are true Algse-feeders ; but when killed, the stomachs of 

 these animals are always found mostly filled with marine weeds. 



" Geological and Geographical Distribution of Petroleum Deposits and Fucoidal 

 Remains, — A last argument, no less conclusive on the subject, is taken from the 

 geological and also from the geographical relation between deposits of petro- 

 leum iiud Fucoidal remains. 



Oil-bearing strata are seen in the Coal Measures mostly inferior to the big 

 bed of coal No. 1, which is often a cannel coal ; and sometimes also, but rarely, 

 at a higher horizon, as, for example, below coal No. 3, and also coal No. 12, 

 generally in more or less evident connection with cannel coal. This has pro- 

 bably led to the opinion, still admitted by some geologists, that all the deposits 

 of petroleum owe their origin to a slow decomposition of coal, under some 

 peculiar influences. As there has not heretofore been observed any indications 

 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 

 phenomenon 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 combustible matter has been formed, especially from the 

 remains of aerial plants, whose tissue was mostly vascular, or vascular and 

 cellular, like that of the Lepidodendron, Sigillaria, 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 Stig- 

 maria and its leaves, the compound, originally half fluid and more easily decom- 

 posed, becomes, by the slow process of combustion, compact, homogeneous, 

 without apparent layers, tending to mere bitumen, thus forming the diflerent 

 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 Breckenridge, 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 



