144 



ESSAY ON CLASSIFICATION. 



in the work. 1 And even now how many important ques- 

 tions still await an answer ! 



One result, however, now stands unquestioned the ex- 

 istence during each great geological era 2 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 strati- 

 fied crust of our globe, the number of which is daily increas- 

 ing as our investigations become more extensive and more 

 precise. 3 What remains to be done is to ascertain with 



sil Shells of the Tertiary Formations 

 of North America ; Philadelphia, 

 1832-36, 8vo., fig. GRATELOUP (Dr.), 

 Conchyliologie fossile du bassin de 

 1'Adour, etc.; Bordeaux, 1837, Svo., 

 fig. MATHERON (Pn.), Catalogue 

 methodique et descriptif des corps 

 organises fossiles, etc. ; Marseilles, 

 1842, 8vo. BERENDT (G. C.), Orga- 

 nische Reste im Bernstein ; Berlin, 

 1845-54, fol., fig. WOOD (S. V.), A 

 Monograph of the Crag Mollusks 

 (Palasont. Soc.), 1848-50, 4to., fig. 

 EDWARDS (F. E.), Eocene Mollusca 

 (Palteont. Soc.); London, 1849-52, 

 4to., fig. HORNESS (M.), Die Fossi- 

 len Mollusken des TertiJir-Beckens 

 von Wien; Wicn, 1851, 4to., fig. 

 BEYRICII (E.), Die Conchylien des 

 norddeutschen Tertiargebirges ; Ber- 

 lin, 1854-57, Svo., fig. TUOMEY (M.), 

 and HOLMES (FR.S.), Fossils of South 

 Carolina; Charleston, 1855-57, 4to., 

 fig. 



1 Btrcn (L. v.), Purifications re- 

 cueillies en Amerique, par M. Alex, 

 de Humboldt et par M. Ch. Dcgen- 

 hard; Berlin, 1838, fol., fig. OR- 

 BIGNY (ALC. D'), Voyage dans I'Amu- 

 rique Meridionale, etc. ; Paris, 1834- 

 43, 7 vols., 8vo., Atl., 4to. ARCHIAC 

 (Vic. D',)et HAIME, (J.,) Description 

 des animaux fossiles du groupe uum- 

 mulitiquede 1'Inde ; Paris, 1853, 4to. 

 fig. LEUCKART, (F. S.,) Ueber die 

 Verbreitung der iibriggebliebenen 

 Rcste einer vorweltlichen Schopfung; 

 Freiburg, 1835, 4to. 



3 Geological text-books : DE LA BE- 

 CHE, (Sir H. T.,) Geological Manual ; 

 London, 1833, 1 vol. Svo. ; German 

 Trans, by Dechen ; French by Bro- 

 chant de Villers. The Geological Ob- 

 server ; London, 1851, 8vo. LYELL, 

 (Sir C.,) Manual of Elementary Geo- 

 logy ; London, 1851, 1 vol. Svo. 

 Principles of Geology, etc. ; London, 

 1830, 2 vols. 8vo. ; 8th edit. 1850, 1 

 vol. Svo. NAUMANN, (C. FR.,) Lehr- 

 buch der Geognosie ; Lepzig, 1850- 

 54, 2 vols. 8vo. Atl. 4to. VOGT, (C.,) 

 Lehrbuch der Geologic und Petre- 

 faktenkunde ; Braunschweig, 1854, 

 Svo. 2 vols., 2d edit. Text-books on 

 Fossils : BRONN, (H. G.,) Letheea 

 Geognostica ; Stuttgart, 1835-37, 2 

 vols. Svo. Atl. fol. ; 3d edit, with FR. 

 ROEMER, 1846, et seq. PICTET, (F. 

 J.,) Traite elementaire de Paleon- 

 tologie, etc. ; Paris, 1844-45, 4 vols. 

 8vo. fig. ; 2de edit. 1853 et seq. 8vo. 

 Atl. 4to. ORBIGNY, (ALC. D',) Cours 

 elementaire de Paleontologie ; Paris, 

 1852, 3 vols. 12mo. GIEBEL, (E. G.,) 

 Fauna der Vorwelt ; Leipzig, 1852, 

 2 vols. 8vo. Allgerneine Palreonto- 

 logie ; Leipzig, 1852, 1 vol. Svo. 

 QOENSTEDT, (F. A.,) Handbuch der 

 Petrefaktenkunde ; Tubingen, 1852, 

 Svo. fig. Unfortunately, there does not 

 exist a single English text-book of 

 Palaeontology. A translation of Pic- 

 tet's and Bronn's works would be par- 

 ticularly desirable. 



3 At first only three great periods 

 were distinguished, the primary, the 



