30 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. I. 



FILICITES, OR FOSSIL FERNS. Cases A. B, C. [1, 2, 3.] This 

 numerous and interesting tribe of vascular cryptogamous 

 plants, the living species of which confer a peculiar elegance 

 on the flora of the countries in which they abound, prevailed 

 in great numbers and variety during the carboniferous period ; 

 several hundred extinct species, belonging to many genera, 

 have been determined. Ferns are distinguished from other 

 vegetables by the peculiar arrangement of the veins of the 

 fronds, and the development, in most species, of the fructifi- 

 cation on their leaves. Although the largest British species 

 scarcely exceeds four or five feet in height, many of the tribe 

 peculiar to hot climates are arborescent, and attain an altitude 

 of thirty or forty feet ; their stems are cylindrical and 

 without branches, and the foliage spreads out from the sum- 

 mit of the tree and expands into an elegant canopy. The 

 leaves on the stems are not persistent, and the petioles soon 

 become detached from their base, and leave permanent cica- 

 trices, or scars, on the trunk ; and these imprints are so 

 durable, and so symmetrically arranged, as to afford characters 

 by which the stem of a tree-fern may easily be recognised in 

 a fossil state ; for though the stem may be pressed quite flat, 

 and its foliage entirely wanting, the configuration and dis- 

 position of the scars afford a certain means of identification. 

 The leaves are characterised by the form, regularity, and 

 peculiar mode of subdivision of the segments, and by the 

 delicacy, evenness, and distribution of the veins or nervures. 

 ^f rom the elegance and diversity of form of the foliage, fossil 

 ferns are the most remarkable and attractive vegetable re- 

 mains in the ancient strata and in the collection before us, 

 a considerable number of the most important and cha- 

 racteristic species are exhibited. The greater part are from 

 the coal deposits, the fern-leaves generally occurring in the 

 schists or shales that form the roof of the beds of coal. 1 

 Many of the strata of shale are made up of carbonized fern- 

 leaves and stems closely pressed together. The roof of a coal 

 mine, when newly exposed, often presents the most interesting 

 appearance from the abundance and variety of leaves, branches, 

 and stems, that appear sometimes in relief, sometimes im- 



1 See " Wonders of Geology," Sixth Edition, pp. 666677 : " On the 

 nature of Coal Deposits." 



