THE ERIAN OR DEVONIAN FORESTS. 



61 



than others, and it is a remarkable fact that the spores of 

 certain cryptogamous plants are of this kind, as we see in 

 the inflammable character of the dry spores of Lycopo- 

 dium ; and we know that the slow putrefaction of such 

 material underground effects chemical changes by which 

 bituminous matter can be produced. There is, there- 

 fore, nothing unreasonable in the supposition advanced 

 by Prof. Orton, that the spores so abundantly contained 

 in the Ohio black shales are important or principal sources 

 of the bituminous matter which they contain. Micro- 

 scopic sections of this shale show that much of its mate- 

 rial consists of the rich bituminous matter of these spores 

 (Fig. 16). At the same time, while we may trace the 

 bitumen of these shales, and of some beds of coal, to this 

 cause, we must bear in mind that there are other kinds of 

 bituminous rocks which show no such structures, and may 

 have derived their combustible material from other kinds 

 of vegetable matter, whether of marine or of land plants. 

 We shall better understand this when we have considered 

 the origin of coal. 



The macrospores above referred to may have belonged 

 to humble aquatic plants mantling the surfaces of water 

 or growing up from the bottom, and presenting little 

 aerial vegetation. But there are other Erian plants, as 

 already mentioned, which, while of higher structure, may 

 be of Rhizocarpean affinities. 



One of these is the beautiful plant with whorls of 

 wedge-shaped leaves, to which the name Sphenophyllum 

 (see Fig. 20) has been given. Plants referred to this 

 genus have been described by Lesquereux from the upper 

 part of the Siluro-Cambrian,* and a beautiful little spe- 

 cies occurs in the Erian shales of St. John, New Bruns- 

 wick, f The genus is also continued, and is still more 



* " American Journal of Science." 



f Dawson, " Report on Devonian Plants," 1870. 



