PART II. CHAPTER XX. 



247 



Fossil Plants of the Coal Strata. 



Fossil Plants of the Coal. — But the flora of the coal forms 

 the most interesting feature in its palseontology, and is far better 

 known to us than any other flora antecedent to the tertiary era. 

 About 300 species of terrestrial plants are enumerated by M. 

 Adolphe Brongniart as proper to the Coal, but botanists have 

 encountered the greatest difficulty in determining the natural 

 affinities of these fossils, it being rare to find in them any vestige 

 of flower, seed, or fruit, those organs which afford the most con- 

 venient characters for classifying living plants. They have been 

 obliged, therefore, first to study more minutely the different 

 forms of bark in existing trees, their various modes of branch- 

 ing, the tissue of their wood, nervures of the leaves, and other 

 peculiarities of vegetable structure which might enable them to 

 institute a direct comparison between the analogous parts of 

 recent and fossil plants.* 



The most common of these vegetable remains may be provi- 

 sionally classed under the following heads : — First, Ferns and 

 Sigillariae ; secondly, Lepidodendra, allied to Lycopodiacecs 7 

 thirdly, Calamites, allied to Equisetacece ? fourthly. Coniferous 

 plants ;■ fifthly, Stigmarise, apparently an extinct family of plants. 



Ferns and Sigillarice. — The leaves, or more properly speak- 

 ing, the fronds, of ferns, (see Figs. 249, 250.) for the most part 

 destitute of fructification, exceed in number all other plants in 

 the shale of the coal. They have been divided by M. Ad. Brong- 

 niart into genera, characterized chiefly by the branching of the 

 fronds, and the way in which the veins of the leaves are dis- 

 posed. These fronds are often accompanied by large -fluted 

 stems or trunks of trees which have been squeezed down and 

 flattened as they lay prostrate in the shale, so that the opposite 

 sides meet, but which when they occur in the accompanying grit 

 or sandstone, and are placed obliquely or vertically to the planes 

 of stratification, are round and uncompressed. Their bark has 

 been converted into coal ; and they must have been hollow when 

 first deposited, for the interior became filled, not only with sand, 

 but with leaves and branches of ferns, introduced from above. 

 Impressions of these fronds are now frequent in the pillars of 

 sandstone, which may be regarded as casts of the interior of 

 those ancient trees. Most of the trunks or stems now alluded 

 to have been called Sigillarise. They vary from half a foot to 

 five feet in diameter, and must have been sometimes forty or fifty 

 feet high. 



It is admitted by all botanists that some of these gigantic 

 stems, all of which are comprehended by Brongniart in his 



* See the works of MM. Ad. Brongniart, Sternberg, and others, and the Fossil 

 Flora of Lmdley and Hutton. 



