54 ESSAY ON CLASSIFICATION. Part I. 



four concentric reefs are only the most distinct of that region ; others, less exten- 

 sively investigated thus far, lie to the northward; indeed, the whole peninsula of 

 Florida consists altogether of coral reefs annexed to one another in the course of 

 time, and containing only fragments of corals and shells, etc., identical with those 

 now livmg upon that coast. Now, if a width of five miles is a ftxir average for one 

 coral reef growing under the circumstances under which the concentric reefs of 

 Florida are seen now to follow one another, and this regular succession should extend 

 only as far north as Lake Ogeechobee, for two degrees of latitude, this would give 

 V about two hundred thousand years for the period of time which was necessary for 



that part of the peninsula of Florida which Ues south of Lake Ogeechobee to rise 

 to its present southern extent above the level of the sea, and durmg Avhich no 

 changes have taken place in the character of the animals of the Gulf of Mexico. 



It is very prejudicial to the best interests of science to confound questions that 

 are entirely diflerent, merely for the sake of supporting a theory ; yet this is con- 

 stantly done, whenever the question of the fixity of species is alluded to. A few 

 more words upon this point will, therefore, not be out of place here. 



I Avill not enter into a discussion upon the question whether any species is found 

 identically the same in two successive formations, as I have already examined it at 

 full length elsewhere,^ and it may be settled finally one way or the other, without 

 affecting the proposition now under consideration ; for it is plain, that if such identity 

 could be proved, it would only show more satisfactorily how tenacious species are in 

 their character, to continue to live through all the physical changes which have 

 taken place between two successive geological periods. Again, such identity once 

 proved, would leave it still doubtful whether their representatives in two successive 

 epochs are descendants one of the other, as we have already strong evidence in favor 

 of the separate origin of the representatives of the same species in separate geo- 

 graphical areas.^ The case of closely allied, but diflerent species occurring m succes- 

 sive periods, yet limited respectively in their epochs, aflbi'ds, in the course of time, a 

 parallel to the case of closely allied, so-called, representative species occupying differ- 

 ent areas in space, wliieh no sound naturalist would suppose now to be derived one 

 from the other. There is no more reason to suppose equally allied species following 

 one another in time to be derived one from the other; and all that has been said 



sideration, to the charming song of Chamisso, entitled Mollusques fossiles, Neuchatel, 1831-45, 4to. fig. — 



Tragishe Geschichte, and beginning as follows: Agassiz, (L.,) Monographies d'Echinodermes vivans 



's war Einer dem's zu Herzen ging. et fossiles, Neuchatel, 1838-42, 4 nos., 4to. fig. — 



* Agassiz, (L.,) Coquilles tertiaires reputees Agassiz, (L.,) Recherches sur les Poissons fossiles, 



identiques avee les especes vivantes, Nouv. Mem. de Neueliutel, 1833-44, 5 vols., 4to., atlas, fol. 

 la Soc. Ilelv. des sc. nat. Neuchatel, 1845, vol. 7, - See Sect. 10, where the case of representative 



4to. fig. — Agassiz, (L.,) Etudes critiques sur les species is considered. 



