GENERAL SUCCESSION OF PLANTS IN TIME. 1 48 5 



present in comparative abundance. Lastly, the Gymnosperms are 

 represented by the woody trunks of Conifers (Dadoxylon). 



The Carboniferous deposits are remarkable for the richness of 

 their contained flora, as also for the extensive development of beds 

 of workable coal. The predominant plants of this period belong to 

 the groups of the Pteridophytes and Gymnosperms. The former 

 are represented by types belonging 

 to the Rhizocarps, the Ferns, the 

 Lycopods, and the Equisetacece ; 

 though in many cases the Car- 

 boniferous plants referred to these 

 groups exhibit quite peculiar char- 

 acters, and their precise affinities 

 are not always clear. The Rhizo- 

 carps are represented by the ancient 

 genus SpheHophyllum and by the 

 macrospores of Protosalvinia. The 

 latter sometimes occur in vast num- 

 bers in the shales of the Carbon- 



. . rig. 1358. — A slice of shale from the 



lferOUS period, and Occasionally play Devonian rocks of Kettle Point, Lake 



, • ,r r .• Huron, showing the "macrospores" of 



an important part 111 the formation Protosahinia. magnified. (Original ) 



of coal, though this must be re- 

 garded as exceptional. The Lycopodiacece, are represented by the 

 genus Lycopodites, but the most remarkable members of this series 

 in Carboniferous times are the tree-like Lepidodendroids (Lepido- 

 dendron, &c.) The great group of the Sigillarioids (Sigillaria, &c), 

 likewise comprising comparatively gigantic plants, is also usually 

 regarded as belonging to the series of the Lycopods, and is highly 

 characteristic of the Carboniferous deposits. The Equisetacece, 

 again, are largely represented in Carboniferous times by the re- 

 markable and widely distributed group of the Calamites. Lastly, 

 the Carboniferous rocks have yielded the remains of a large 

 number of true Ferns, which, in most essential respects, are similar 

 to the existing types of the group. 



No unquestionable Angiosperms have hitherto been detected in 

 rocks of Carboniferous age, but the Gymnosperms are represented 

 by various Conifers (Dadoxylon, Araucarioxylon, and Pinites). 



It is universally admitted that coal is fossilised vegetable matter, and 

 also that, in general, the vegetation which formed the coal grew where 

 the coal-seam is now found. The problem of the precise mode in which 

 the coal-seams of the Coal-measures were fonned is largely a geological 

 one, and need not be discussed here. It is sufficient to say here that 

 coal is the result of the bituminisation of vegetable tissues of different 

 kinds, different coal-seams, or different portions of a single seam, being 

 often unlike in their precise structure or mode of formation. According 

 to the researches of Sir William Dawson, the microscopic examination 



