96 



ESSAY ON CLASSIFICATION. 



Part I. 



One result, however, stands now unquestioned: the existence during each great 

 geological era^ of an assemblage of animals and plants differing essentially for each 

 period. And by period I mean those minor subdivisions in the successive sets 

 of beds of rocks, which constitute the stratified crust of our globe, the number of 

 which is daily increasing, as our investigations become more extensive and more 

 precise.^ What remains to be done, is to ascertain with more and more precision, 

 the true aflftnities of these remains to the animals and plants now living, the rela- 

 tions of those of the same period to one another, and to those of the preceding 

 and following epochs, the precise limits of these great eras in the development 

 of life, the character of the successive changes the animal kingdom has undergone, 

 the special order of succession of the representatives of each class,^ their combina- 



(Vic. d',) et Hai.me, (J.,) Description des animaux 

 fossiles du groupe nummulitique de I'lnde, Paris, 

 1853, 4to. fig. — Leuckart, (F. S.,) Ueber die 

 Verbreitung der ubriggebliebenen Reste einer vor- 

 weltlichen Schopfung, Freiburg, 1835, 4to. 



^ Geological text-books: DelaBeche, (Sir H.T.,) 

 Geological Manual, London, 1833, 1 vol. 8vo. ; Ger- 

 man Trans, by Dechen ; French by Brocbant de Vil- 

 lers. — The Geological Observer, London, 1851, 8vo. 

 — Ltell, (Sir C.,) Manual of Elementary Geology, 

 London, 1851, 1 vol. Svo. — Principles of Geology, 

 etc., London, 1830, 2 vols. 8vo. ; 8th edit., 1850, 

 1 vol. Svo. — NAtrsiANN, (C. Fr.,) Lehrbuch der 

 Geognosie, Leipzig, 1850-54, 2 vols. 8vo. Atl. 4to. — 

 VoGT, (C.,) Lehrbuch der Geologic und Petrefalsten- 

 kunde, Braunschweig, 1854, 8vo. 2 vols., 2d edit. — 

 Text-books on Fossils: Bronn, (H. G.,) Lethtea 

 Geognostica, Stuttgart, 1835-37, 2 vols., 8vo. Atl. 

 fol. ; 3d edit, with Fr. R^emer, 1846, et seq. — 

 PiCTET, (F. J.,) Ti-aite elomentaire de Paleontologie, 

 etc., Paris, 1844-45, 4 vols., 8vo. fig.; 2de edit. 1853 

 et seq., Svo. Atl. 4to. — Orbignt, (Alc. d',) Cours 

 elementaire de Paleontologie, Paris, 1852, 3 vols., 

 12mo. — GiEBEL, (E. G.,) Fauna der Vorwelt, Leip- 

 zig, 1852, 2 vols. Svo. — Allgemeine Pateontologie, 

 Leipzig, 1852, 1 vol., Svo. — Quenstedt, (F. A.,) 

 Handbuch der Petrefaktenkunde, Tubingen, 1852, 

 Svo. fig. Unfortunately, there exists not a single 

 English text-book of Paltrontology. A translation 

 of Pictet's and Bronn's works would be particularly 

 desirable. 



^ At first, only tliree great periods were distin- 

 guished, the primary, the secondary, and the tertiary ; 

 afterwards, six or seven, (DelaBeche) ; later, from 

 ten to twelve ; now, the number is almost indefinite, 

 at least undetermined in the present stage of our 

 knowledge, when many geologists would only con- 

 sider as subdivisions of longer periods, what some 

 paleontologists are inclined to consider as distinct 

 periods. 



^ The principal Monographs relating to special 

 classes or families, are the following ; Polyps and 

 Infusoria : Michelin, (H.,) Iconographie Zoophy- 

 tologique, Paris, 1841-45, 4to. fig. — Edwards, (H. 

 Milne,) et Haime, (J.,) Recherches, etc., q. a., p. 31. 

 — Polypiers fossiles des terrains palt5ozoiques, Arch. 

 Mus., vol. 5. — Monograph of the British Fossil 

 Corals, Palfeont. Soc, London, 1850-55, 4to. fig. — 

 Lonsdale, (W.,) On the Corals from the Tertiary 

 Formations of North America, Journ. Geol. Soc, I., 

 p. 495; Sill. Journ., 2d ser. IV., p. 357. — McCoy, 

 (Fr.,) Contributions to British Palieontology, Cam- 

 bridge, 1854, 1 vol. Svo. fig. — References to all 

 minor papers may be found in Edwards and Haime's 

 Recherches. — Ehrenberg, (C. G.,) Mikrogeologie, 

 Leipzig, 1854, fol. fig. — Echinoderms: Miller, (J. 

 C.,) a Natural History of the Crinoidea, Bristol, 

 1821, 4to. fig. — Orbignt, (Alc. d',) Histoire 

 naturelle generale et particuliere des Crinoides vivans 

 et fossiles, Paris, 1840, 4to. fig. — Austin, (Th. and 

 Th. Jr.,) Monograph on Recent and Fossil Crinoidea, 

 Bristol, 4to. fig. (without date.) — Hall, (.L,) 



