150 ESSAY ON CLASSIFICATION. 



the succession of their representatives, in different periods, 

 agrees with their respective standing, as determined by 

 the gradation of their structure. 



Among plants, we find in the Carboniferous period Ferns 

 and Lycopodiaceae prominent; 1 in the Triassic period, 

 EquisetaCeae 2 and Coniferae prevail; in the Jurassic depo- 

 sits, Cycadeae 3 and Monocotyledonese ; while later only 

 Dicotyledoneae take the lead. 4 The iconographic illustra- 

 tion of the vegetation of past ages has of late advanced 

 beyond the attempts to represent the characteristic fea- 

 tures of the animal world in different geological periods. 5 



Without attempting here to characterize this order of 

 succession, so much already follows from the facts men- 

 tioned, that, while the material world is ever the same 

 through all ages in all its combinations as far back as 

 direct investigations can trace its existence, organized 

 beings, on the contrary, ever transform these same mate- 

 rials into new forms and new combinations. The carbon- 

 ate of lime of all ages is the same carbonate of lime in 

 form as well as in composition, as long as it is under the 

 action of physical agents only. Let life be introduced 

 upon earth, and a Polyp builds its coral out of it, and 

 each family, each genus, each species, a different coral, which 

 is again different in'every successive geological epoch. Phos- 

 phate of lime in palaeozoic rocks is the same phosphate as 

 when prepared artificially by Man ; but Fishes make their 



1 See, above, p. 141. der Vorwelt ; Leipzig, 1841, 4to. fig. 



3 SCHIMPER (W. P.), et MOUGEOT HEER(0.),Flora tertiaria Helvetia, 



(A.) Monographic des Plantes Fos- Wintherthur, 1855, fol. fig. 



siles du Gres-bigarre de la chaine 4 Landscapes of the different geo- 



des Vosges, Strasb. et Paris, 1840- logical periods are represented in 



43, 4to. fig. UNGER (Fn.), Die Vorwelt in ihren 



3 BUCKLAND (W,), On the Cyca- verschiedenen Bildungsperioden, 



deoidfe, a Family of Plants found in Wien,fol.(no date.) These landscapes 



Oolite, etc., Trans. Geol. Soc. Lond. are ideal representations of the vege- 



2d ser. II., p. 395. UNGER (FR.), tation of past ages. 

 Chloris protogsea, Beitrage zur Flora 



