FOSSIL PLANTS. 489 



sippi and Ohio, where fossilized wood is found generally associated with a fer- 

 ruginous argillaceous sandstone, is there any trace of volcanic agency. There 

 is merely an evident relation of this kind of fossilization with the deposition of 

 iron. In Ohio and Virginia, that part of the Mahonmg sandstone containing 

 silicified trunks, borders, and perhaps overlays in part, the area where the 

 richest and most numerous beds of iron ore have been deposited. In the re- 

 cent formations, the fossilized wood is generally associated with the red or fer- 

 ruginous clay. Even in the small area occupied by our Post Tertiary forma- 

 tion at Barlow, Ohio, disks of silicified fossil wood of dicotyledonous species 

 are found in a bed of red ferruginous clay, associated with species of shells of 

 the genus Anodonta, entirely transformed into a compact mass of oxyd of iron. 



5. THE FLORA OF THE CARBONIFEROUS MEASURES OF 

 ILLINOIS, CONSIDERED IN SOME OF ITS AFFINITIES. 



As a whole, the coal flora of Illinois has, like that of our American Coal 

 Measures, the general character of the Carboniferous flora of the whole world. 

 It is well known that the representatives of this flora mostly pertain to a single 

 class of vegetables : that of the acrogenous or vascular cryptogamous plants, 

 containing the three families of Equisetacese, FUices and Lycopodiacese. The 

 .nodules of Mazon creek, where fragments of plants, even of the softest texture, 

 have been preserved in their integrity, offered a good opportunity for examin- 

 ing the often proposed question : whether plants of a lower or of a higher order 

 than those could not have entered into the compound of the coal, and, from a 

 peculiar consistance of tissue, have been destroyed by maceration, without* leav- 

 ing any traces of their primitive forms. This has been affirmed, for example, 

 of the Algsp, or marine plants, which have left their remains in abundance in 

 the Lower Carboniferous and Devonian strata, and also of the small cellular 

 vegetables, Fungi and Lichens, which, at the present time, live on the bark of 

 the trunks and branches of our trees, and are also observable, in the same cir- 

 cumstances, in the Tertiary and Cretaceous formations. I have already re- 

 marked, that no remains of any kind of marine plants have as yet been observed 

 in the concretions of Mazon creek.* This is the more noticeable, as some of 

 them have for nuclei bones of fishes of moderate size. As the so-called 

 Fucoides have also never been seen in any bed of shale overlying coal strata, it 

 is reasonable to conclude that the remains of these plants have not contributed 



*Since this report was written, two or three nodules have been obtained from Mazon creek, 

 inclosing marine shells, one of which is an Aviculopecten, and the others probably referable to 

 the genera Nucula and Polyphemopsis or Macrochdlus, and indicate that these Mazon creek 

 shales were probably an estuary deposit, in which the remains of marine animals were sparingly 

 intermingled with the fauna and flora of the adjacent land. A. H. W. 



62 



