480 PALEONTOLOGY OP ILLINOIS. 



water, and having for a larger proportion of their compound, broken remains of 

 organized beings. In this case the remains are either animal or vegetable 

 mixed together, both fragments of moluscs and fishes with fragments of plants 

 recognizable on the same piece of shale, or mere remains of animals or only 

 plants. These various appearances are easily explained in considering the phe- 

 nomena accompanying the formation of tha coal strata, from deposits analo- 

 gous to those of our existing peat bogs. For the surface of these bogs, even 

 in our time, shows the same differences in the superposed deposits, according 

 to the depth and chemical compounds of the water by which they become 

 covered, either by casual inundation in the interior of the land, or by slow ini. 

 mersion near the borders of lakes or sea shores. Even where the coal and shales, 

 from the amount of remains of fishes which they contain, appear to have been 

 formed in water of a certain depth, the matter always bears evident traces of 

 its origin from land vegetation, and never from marine plants. The lower part 

 of a bed of coal, worked near the mouth of Yellow creek, Ohio, is a kind of 

 cannel coal, or very bituminous compact shale, full of the remains of fishes, 

 whose entire skeletons vary in length from one inch to one foot. Yet this shale 

 has an abundance of the remains of land plants mixed in its compound. The 

 same case is observable in Kentucky for example, at Airdrie, on Green river, 

 where the upper coal (No. 11 of the Kentucky section,) is overlaid by a bitu- 

 minous laminated shale, containing teeth of large fishes with trunks of Sigil- 

 laria, Lepidodendron, etc., and branches and leaves of ferns. Those who have 

 examined our immersed peat bogs along the shores of New Jersey, have seen 

 in activity a formation of the same kind, where logs of large trees are fished 

 from a depth often or fifteen feet, out of beds of peat submerged in water deep 

 enough to feed a variety of fishes ; while here and there, small islands, half float- 

 ing fragments of wood or heaps of mud, are covered with a luxuriant growth 

 of ferns, reeds or bushes, which throw their debris to the surface, to be con- 

 veyed to the bottom and there mixed in the bed of rnud, an incipient shale, 

 with animal remains. 



Among the various metamorphoses to which remains of plants have been 

 subjected in the shale by compression, decomposition and other chemical and 

 mechanical agencies, one peculiar phenomenon is worth noticing here. In the 

 shale covering the bed of anthracite of Rhode Island, the whole carbonaceous 

 matter of the plants has been destroyed by heat, and the mere skeleton of the 

 leaves and other remains is marked upon the shale as a more or less distinct 

 mould, often covered by a whitish incrustation of selenite. In this process of 

 fusion, the vegetable fragments have been distorted in such a way that they 

 often present an appearance far different from that of the species to which they 

 belong. For example, in some branches of ferns, the leaflets have been, on 

 one side of the pinnae, extended to double their original length, and narrowed 



