4G6 PALAEONTOLOGY OF ILLINOIS. 



the Millstone grit (from the Chester group of the Subcarbonif- 

 erous series) . The plants collected in Randolph and Pope coun- 

 ties, though found in the Subcarboniferous measures, are mostly 

 species of Lepidodendron, Knorria and Stigmaria. All are of 

 the true Carboniferous type; some of them even, especially all 

 the Stigmaria, ascend high in the true Coal Measures above 

 the millstone grit, thus indicating for the low coal an identity 

 of formation by an identical vegetation. 



2d. That the predominance of large vegetables of the 

 Lycopodiaceae, viz: The Lepidodendran is remarkable in these 

 Subcarboniferous strata of Illinois, and strengthen the conclu- 

 sion already taken from the examination of the Coal Measures 

 of other States : that the flora of the lower coal was essentially 

 composed of large species of Lepidodendron, and that these were 

 subsequently replaced by other species or' genera. To confirm 

 this opinion we have only to compare the Subcarboniferous 

 fossil flora of Pope county with that of Colchester, Duquoin 

 and Mazon creek, three coals whose geological horizon is near 

 the base of the Mahoning sandstone. Here we have scarcely 

 any species of Lepidodendran, a few Sigillaria of the section of 

 the Leiodermaria, and of small size, and a proportionally very 

 large number of ferns. This peculiar distribution of fossil re- 

 mains of plants being, in Illinois, in perfect accordance with 

 what has been observed in the Coal Measures of other States, 

 evidently shows that the varieties of vegetation are not due to 

 peculiar and local influences, or to peculiar botanical zones, but 

 are truly in concordance with the different horizons of the Coal 

 Measures, and thus indicate successive or different formations. 

 If, then, we were all to study and to know the plants which 

 have contributed to the formation of each bed of coal, the re- 

 mains of these plants, when found in the shales, would always 

 indicate a peculiar horizon. 



3d. The examination of the coal flora of Illinois proves the 

 identity of vegetables in the whole American coal fields. The 



