80 ESSAY ON CLASSIFICATION. 



four concentric reefs are only the most distinct of that 

 region; others, thus far less extensively investigated, 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 living 

 upon that coast. Now, if a width of five miles is a fail- 

 average for one coral reef, growing under the circum- 

 stances under which the concentric reefs of Florida are 

 seen now to follow one another, and this regular succes- 

 sion extends only as far north as Lake Ogeechobee, 

 for two degrees of latitude, this would give about two 

 hundred thousand years for the period of time which was 

 necessary for that part of the peninsula of Florida which 

 lies south of Lake Ogeechobee to rise to its present 

 southern extent above the level of the sea, and during 

 which no changes have taken place in the character of 

 the animals of the Gulf of Mexico. 1 



It is very prejudicial to the best interests of science to 

 confound questions that are entirely different, merely for 

 the sake of supporting a theory ; and yet this is constantly 

 done, whenever the question of the fixity of species is 

 alluded to. A few more words upon this point, therefore, 

 will not be out of place here. 



I will not enter into a discussion upon the question, 

 whether any species are found identically the same in two 

 successive formations, as I have already examined it at 

 full length elsewhere, 2 and it may be settled finally, one 



sicleration, to the charming song of 3 AGASSIZ (L.), Coquilles tertiaires 



Chamisso, entitled Tragische Qes- reputees identiques avec les especes 



chichte, and beginning as follows : vivantes ; Nouv. Mem. de la Soc. 



"'s war Einer dem'szu Herzenging." Helv. des sc. nat., JSTeuchatel, 1845, 



1 According to facts recently ob- vol.7,4to., fig. AOASSIZ (L.), Etudes 



served, and alluded to above, double critiques sur les Mollusques fossiles ; 



that time, at least, has elapsed since Neuchatel, 1831-45, 4to., fig. AGAS- 



their first appearance in these waters, siz (L.), Monographies d'Echino- 



