722 NOMENCLATUKE OF FOSSIL PLANTS. 



, 2. Acrogenous Ciyptogamous Plants, comprehending two classes, Muscl and 

 Filicales ; the latter being divided into flye families— Ferns, MarsUeaceffi, Chara- 

 cese, Lycopodiacese, and Bquisetaoese. 



3. Dicotyledouons Phanerogamous Plants, of which he enumerates the several 

 families, indicating the characters which show their aifinity to the same families 

 of living vegetahles. 



4. Monocotyledonous Plants. ! 



When the analogy between a fossil and a living plant is such that 

 the difference is not greater than occurs among the individuals in- 

 cluded 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, as Alnus primseva, Quercus Lignitum, 

 Ulmus Bronnii, and Pinus Palseostrobus. If the differences are well 

 marked, but at the same time the organ which represents them is not 

 of sufficient importance 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 is a 

 genus allied to Zamia, Thuites to Thuia, Taxites to Taxus. If a 

 fossil plant, although presenting several essential characters of a family, 

 yet differs in the fossilised 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 different from those actually 

 existing. This will be seen in many of the coal fossils, as Sigillaria 

 and Lepidodendron. 



The rocks of which the globe is composed are divided into two 

 great classes, those which contain fossil remains, and which are called 

 Fossiliferous, and those having no such remains, and which are 

 designated Non-fossiliferous or Azoic (a, privative, and ^w^, life). 

 The igneous unstratified rocks, included under the names of Granitic 

 and Trappean, show no appearance of animal or vegetable remains. 

 Trap rocks, however, have in some cases covered or enclosed vegetable 

 structures, and these are found in an altered condition. Thus, in Antrim, 

 near the Giant's Causeway, deposits containing vegetable remains occur 

 interstratified with basaltic rocks. These remains are of miocene age, 

 and have been referred to coniferous plants, beeches, oaks, plane-trees, 

 etc. Plants of the same kind have been discovered in a simi- 

 lar position by the Duke of Argyll in the island of Mull. In trap 

 rocks near Edinburgh, lignite with distinct structure has also been 

 detected. Several beds of ash formed into solid compact rock by in- 



