76 On the Vegetation of the Carboniferous Period, 



attached to those roots in soils similar to the under-clays, but uncon- 

 nected with any seam of coal. These stumps are almost universally 

 erect, — are uniformly scattered over the seams, and otherwise appear 

 to have decidedly grown on the surface of the coal ; the shales like- 

 wise seem deposited between these stumps. The rarity of Sigillarice 

 roots (Stigmarise) in this position, is probably due to their being in- 

 corporated with the coal itself, though they sometimes occur above 

 that mineral, and between the layers of shale. The seams of iron- 

 stone (or black band) are the last modifications of soil by vegetable 

 matter, to which allusion has been made : when these are uniform 

 beds or layers, they may be supposed to be the deposit from water 

 charged with iron and soil which has percolated through the peat, 

 and in so doing absorbed a great deal of vegetable matter. The 

 layers of nodular iron-stone are simple modifications of these, and 

 may be caused by the sedimentary particles contained in the fluid, 

 which, instead of being deposited in a uniform stratum, are aggre- 

 gated round broken bits of vegetable matter (as fern-leaves, stems, or 

 cones) which served as nuclei. 



Now, though each of these points admits of some explanation when 

 taken independently, and some illustration from the action of an ex- 

 isting vegetation upon soil, &c., it is very difficult to understand their 

 combined operation over so enormous a surface, for instance, as one 

 of the American coal-fields, and even more to account for their re- 

 gular recurrence, according to some fixed law, in every successive 

 coal-seam throughout the whole carboniferous formation. These are 

 problems of the highest order, and unsuited to this sketch, the re- 

 mainder of which shall refer to the plants themselves, and especially 

 to those botanical characters according to which the Coal Flora has 

 been grouped and named, and to an illustration of these several 

 points, by a comparison of them with what are afi^orded of recent 

 plants. 



On the probable extent of the Flora of the Coal-Formation in Britain. 



No fewer than 300 species of plants have been enumerated as 

 belonging to the Coal Flora of Great Britain ; but, whether this gives 

 any approximation either to what was the amount of their species 

 at one period, or even to all those which contribute to form the coal, 

 it is impossible to say. It need hardly be observed, that a collection 

 of the fragments imbedded in our most recent deposits is no index 

 to the general mass of the vegetation, nor are the remains neces- 

 sarily those of the commonest plants, or even of such as would d, 

 priori be judged the best suited for becoming fossilised. That 

 hitherto unknown species do exist in an available state for the botanist 

 cannot be doubted; they are of frequent occurrence ; but that these are 

 not ^c numerous as might be expected from the enormous magnitude 

 of a coal-field, is evident from the great uniformity that prevails 

 throughout the formation. It may indeed be a query, whether the 



