IMMUTABILITY OF SPECIES. 79 



to which we belong is still a problem, notwithstanding the 

 precision with which certain systems of chronology would 

 fix the creation of man. 1 There are, however, many cir- 

 cumstances 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, 2 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 sur- 

 face of the ocean. There are, around the southernmost 

 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 (nay, 

 probably, over one hundred thousand years) ; and yet the 

 the corals by which they were all built up are the same 

 identical species in all of them. These facts, then, fur- 

 nish evidence as direct 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, 3 and have not undergone the slightest 

 change during the whole of that period. 4 And yet these 



1 NOTT and GLIDDON, Types of at one hundred thousand years; so 



Mankind, p. 653. slow are the operations of nature. 



3 See my paper upon the Reefs of 4 Those who feel inclined to ascribe 



Florida, soon to be published in the the differences which exist between 



Reports of the United States Coast species of different geological periods 



Survey, extracts of which are already to the modifying influence of physi- 



printed in the Report for 1851, p. 145. cal agents, and who look to the 



A renewed examination of the reefs changes now going on among the liv- 



of Florida has satisfied me that this ing for the support of such an opi- 



estimate falls short of the reality by nion, and not being satisfied that the 



a great deal. The rate of growth of facts just mentioned are sufficient 



the corals, ascertained by direct ob- to prove the immutability of spe- 



servation, is not half so rapid as I cies, still believe that a longer 



had been led to assume at first. period of time would yet do what 



3 I am now satisfied that the age of thirty thousand years have not done, 



this reef is not overstated, if estimated I beg leave to refer, for further con- 



