FUNDAMENTAL RELATIONS OF ANIMALS 61 



man.'^^ There are, however, many circumstances which show that the 

 animals now living have been for a much longer period inhabitants 

 of our globe than is generally supposed. It has been possible to trace 

 the formation and growth of our coral reefs, especially in Florida,^- 

 with sufficient precision to ascertain that it must take about eight 

 thousand years for one of those coral walls to rise from its foundation 

 to the level of the surface of the ocean. There are around the south- 

 ernmost extremity of Florida alone four such reefs concentric with 

 one another, which can be shown to have grown up one after the 

 other. This gives for the beginning of the first of these reefs an age 

 of over thirty thousand years; and yet the corals by which they were 

 all built up are the same identical species in all of them. These facts, 

 then, furnish as direct evidence as we can obtain in any branch of 

 physical inquiry that some, at least, of the species of animals now 

 existing have been in existence over thirty thousand years^^ and have 

 not undergone the slightest change during the whole of that period.^^ 

 And yet these four concentric reefs are only the most distinct of that 

 region; others, less extensively investigated thus far, lie to the north- 

 ^vard; indeed, the whole peninsula of Florida consists altogether of 

 coral reefs annexed to one another in the course of time and contain- 

 ing only fragments of corals and shells, etc., identical with those now 

 living upon that coast.^^ Now, if a width of five miles is a fair aver- 

 age for one coral reef grooving under the circumstances under which 

 the concentric reefs of Florida are seen now to follow one another, 



^^ Nott and Gliddon, Types of Mankind, p. 653. 



®^ See "Extract from the Report of Professor Agassiz . . . ," United States Coast 

 Survey, Annual Report . . . 1851 (Washington, 1852), pp. 145-160. A renewed examina- 

 tion of the reefs of Florida has satisfied me that this estimate falls short of the reality 

 by a great deal. The rate of growth of the corals, ascertained by direct observation, is 

 not half so rapid as I had been led to assume at fust. 



^ I am now satisfied that the age of this reef is not overstated if estimated at one 

 hundred thousand years, so slow are the operations of nature. 



^ Those who feel inclined to ascribe the differences which exist between species of 

 different geological periods to the modifying influence of physical agents, and who 

 look to the changes no^v going on among the living for the support of such an opinion, 

 and may not be satisfied that the facts just mentioned are sufficient to prove the im- 

 mutability of species, but may still believe that a longer period of time would yet 

 do what thirty thousand years have not done, I beg leave to refer, for further con- 

 sideration, to the charming song of Ludovici de Chamisso, entitled Tragishe Geschichte, 

 and beginning as follows: " 's war Einer dem's zu Herzen ging." 



^ [Agassiz's complete account of his Florida researches was published posthumously 

 as "Report on the Florida Reefs . . . ," Bulletin, Museum of Comparative Zoology, 

 VII (1882), whole no.] 



