100 



ESSAY ON CLASSIFICATION. 



Part I. 



a few examples for further discussion. Among Echinoderms the Crinoids are, for 

 a long succession of periods, the only representatives of that class; next follow 

 the Starfishes, and next the Sea-Urchins, the oldest of which belong to the type 

 of Cidaris and Echinus, followed by Clypeastroids and Spatangoids. No satisfactory 

 evidence of the existence of Holothurite has yet been found. Among Crustacea, 

 a comparison of the splendid work of Barrande^ upon the Silurian Sj'stem of 

 Bohemia, with the paper of Count Miinster upon the Crustacea of Solenhofen,^ and 

 with the work of Desmarest upon fossil Crabs,^ will at once show that while 

 Trilobites are the only Crustacea of the oldest palaeozoic rocks, there is found in 

 the Jurassic period a carcinological fauna entirely composed of Macrura, to which 

 Brachyura are added in the tertiary period. The formations intermediate between 

 the older palteozoic rocks and the Jura contain the remains of other Entomostraca, 

 and later of some Macroura also. In both classes the succession of their repre- 

 sentatives, in dift'erent periods, agrees with their respective standing, as determined 

 by the gradation of their structure. 



Among plants, we find in the Carboniferous period prominently. Ferns and 

 Lycopodiaceaj ; * in the Triassic period Equisetacere ^ and Coniferse prevail ; in the 

 Jurassic deposits, Cycadeae,^ and Mouocotyledonea? ; while later only Dicotyledoneae 

 take the lead.'^ The iconographic illustration of the vegetation of past ages has 

 of late advanced beyond the attempts to represent the characteristic features of 

 the animal world in difterent geological periods.^ 



Without attempting here to characterize this order of succession, this much follows 

 already from the facts mentioned, that while the material world is ever the same 

 through all ages in all its comljinations, as fai' back as direct investigations can 

 trace its existence, organized beings, on the contrary, transform these same mate- 

 rials into ever new forms and new combinations. The carbonate of lime of all 

 ages is the same carbonate of Ihne in form as well as composition, as long as it 

 is under the action of physical agents only. Let life be inti'oduced upon earth, 



^ Barrande's Syst. Silur., q, a., p. 23. 



^ Gr. G. v. Munster, Beitrage zur Petrefacten- 

 kunde, q. a., p. 98. 



^ Desmarest, see Brongniart and Desmarest's 

 Hist. Nat. d. Tril. et Crust., q. a., p. 97. 



* See, above, p. 93. 



^ ScHiMPER, (W. P.,) et MouGEOT, (A.,) Mono- 

 graphie des Plantes Fossiles du Gri-s-bigarre de la 

 chaine des Vosges, Strasb. et Paris, 1840—13, 4to. 



fig- 



* BucKLAND, (W.,) On the Cycadeoidae, a Family 



of Plants found in the Oolite, etc., Trans. Geol. Soe. 

 Lond. 2d ser. II., p. 395. 



' Unger, (Fr.,) Chloris protogtea, Beitrage zur 

 Flora der Vorwelt, Leipzig, 1841, 4to. fig. — IIeer, 

 (O.,) Flora tertiaria Helvetian, Wintherthur, 1855, 

 fol. fig. 



* Landscapes of the different geological periods 

 are represented in Unger, (Fr.,) Die Vorwelt in 

 ihren vershiedenen Bildungsperioden, AVien, fol. (no 

 date.) These landscapes are ideal representations of 

 the vegetation of past ages. 



