596 FOSSIL PLANTS OF THE CARBONIFEROUS SYSTEM. 



An exception to this, however, occurs in the Lignite noticed by Miller. 

 It is in the argillaceous and sandy beds of the Carboniferous system, 

 we first meet with decided proofs of the existence of land plants. 

 These strata and sands alternate with beds of Coal, a mineral which is 

 of vegetable origin, and which is deposited in various quarters of the 

 globe in hollow troughs, the layers varying from the thickness of a few 

 inches to 10 or 20 feet. It is rare to find coal exhibiting vegetable 

 structure under the microscope; but in certain cases this may be 

 evidently seen. I have seen it in the Arniston coal of this neighbour- 

 hood. Some have maintained that each stratum of coal is the pro- 

 duct of a peculiar vegetation, frequently different from that which 

 precedes, and from that which follows it. Hence each stratum is 

 often characterized by the predominance of certain impressions. In 

 examining a coal seam, there are frequently evidences of three distinct 

 phases. In the underclay there are roots permeating the mass ; then 

 comes the coal, which is either formed out of the plants whose roots 

 are in the clay, or of others which have grown with them, or have been 

 drifted; and lastly, above the coal there is the shale, which appears 

 to have supported a vigorous vegetation. There have been 300 

 species of plants noticed as belonging to the Coal Flora of Britain. 



1180. Fossil Plants of the Carboniferous System. The great mass 

 of fossil plants of this system belong to Acrogenous Cryptogamics and 

 Dicotyledonous Gymnosperms. Some of the plants called Palms, such 

 as Noggeraihia, Flabellaria, and Artisia, are referred by Brongniart to 

 the latter division. Ferns abound in this system, especially in the clays, 

 ironstones, and sandstones. The species are included under the genera 

 Sphenopteris, Pecopteris, Neuropteris, Odontopteris, Cyclopteris, Glossop- 

 teris, and Lonchopteris. These plants rarely exhibit any traces of fruc- 

 tification, in consequence of only one surface of the fronds being exposed 

 to view, and they are therefore distinguished chiefly by the shape and 

 venation of their fronds. Thus, Sphenopteris (a<pqv, a wedge, and vrko^, 

 a fern), has a bi-tripinnatifid frond, pinnae narrowed at the base (cune- 

 ate), not adherent to the rachis, lobed, veins bipinnate, somewhat radi- 

 ating from the base (fig. 793). In Pecopteris (vk*.u, I comb), the frond 

 is pinnatifid or bi-tripinnatifid, pinnae adnate to the rachis, sometimes 

 confluent, a strong primary vein reaching the apex, the secondary 

 veins being nearly straight, simple or forked, rarely pinnate, sori 

 rounded at the end of the secondaty veins (fig. 794). In Neuropteris 

 (utv^ov, a nerve), the frond is pinnare or bipinnate, pinnae subcordate at 

 the base, distinct from the rachis, strong primary vein vanishing to- 

 wards the apex, secondary veins oblique, arched, repeatedly dichoto- 

 mous (fig. 795). Tree-ferns appear to have existed in Britain during 

 the deposit of the coal strata, and to have occupied an important place 

 in the flora. The stems of these ferns are included under the genus 

 Caulopteris. The fronds have not been found attached; but it is 



