FOSSILIFEROUS STRATIFIED ROCKS. 593 



in most instances require the formation of new genera. While those 

 of the older strata, in numerous instances, cannot be classed in existing 

 families, and must constitute new groups. Such are the Calamites, Lepi- 

 dodendrons, and Sigillarias of the coal formation. From all the investi- 

 gations of fossil botanists, however, it appears that the same great 

 types existed in a former state as at the present day, viz., Cellular 

 Cryptogamics, Vascular Cryptogamics or Acrogens, Monocotyledons 

 and Dicotyledons, both Angiospermous and Gymnospermous. 



1173. Schlotheim, Sternberg, Brongniart, and others, have pro- 

 posed arrangements of fossil plants. That of Brongniart is founded 

 on the resemblances which the fossils bear to living plants. When 

 the analogy between a fossil and a living plant is such, that the differ- 

 ence is not greater than occurs among the individuals included in a 

 species of the living genus, then the fossil and living plant may be 

 considered identical, and the epithet of fossil is applied to the name of 

 the plant. If, on the other hand, the fossil presents distinct specific 

 characters, but does not differ more from living species than these 

 species differ among themselves, then it is looked upon as a new 

 species of the genus. If the differences are well marked, but at the 

 some time the organ which represents them is not of sufficient impor- 

 tance to induce the belief that the plant differs from others of the 

 genus in all its essential organs, then the termination ites is added to 

 the name of the genus. Thus, Lycopodites is a genus of fossil plants 

 allied to Lycopodium, apparently not differing, so far as known, in 

 essential and important parts; so also Zamites allied to Zamia, 

 Thuyites to Thuya. If a fossil plant, although presenting several 

 essential characters of a family, yet differs in the fossilized organ from 

 all the known genera of the family, as much or more than these genera 

 do among themselves, then it is to be considered as a new genus dif- 

 ferent from those actually existing. This will be seen in many of the 

 coal fossils. 



1174. Before proceeding to notice some of the more important 

 fossil plants, it will be necessary to give a sketch of the geological con- 

 stitution of the globe. The rocks of which the earth is composed are 

 either stratified or unstratified ; and the former are either fossiliferous 

 or non-fossiliferous (azoic). The unstratified rocks, included under 

 the names of Granitic and Trappean, are considered igneous, plutonic, 

 or eruptive rocks, and do not exhibit any fossiliferous deposits. 

 Neither do fossil plants occur in certain metamorphic rocks, such as 

 Gneiss and Mica-slate, which present a stratified appearance, and 

 appear to have been deposited in peculiar circumstances, probably at 

 a high temperature. The igneous and metamorphic rocks are some- 

 times included under the comprehensive name of Hypogene. 



11 75. The FossiUferons stratified Rock* have been divided into 1. 

 Palaeozoic (**/<>>, ancient, and fry, life), or those which contain the 



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