44 CORAL REEFS OF FLORIDA. CHAP. xir. 



1846, I cannot form an opinion as to the value of the chrono- 

 logical calculations which have led Dr. Dowler to ascribe to 

 this skeleton an antiquity of 50,000 years. In several sec- 

 tions, both natural in the banks of the Mississippi and its 

 numerous arms, and where artificial canals had been cut, I ob- 

 served erect stumps of trees, with their roots attached, buried 

 in strata at different heights, one over the other. I also re- 

 marked that many cypresses which had been cut through 

 exhibited many hundreds of rings of annual growth, and it 

 then struck me that nowhere in the world could the geologist 

 enjoy a more favorable opportunity for estimating in years 

 the duration of certain portions of the recent ejjoch.* 



Coral Beefs of Florida. 



Professor Agassiz has described a low portion of the penin- 

 sula of Florida as consisting of numerous reefs of coral, which 

 have grown in succession so as to give rise to a continual 

 annexation of land, gained gradually from the sea in a 

 southerly direction. This growth is still in full activitj', and 

 assuming the rate of advance of the land to be one foot in a 

 century, the reefs being built up from a depth of seventy-five 

 feet, and that each reef has in its turn added ten miles to the 

 coast, Professor Agassiz calculates that it has taken 135,000 

 years to form the southern half of this peninsula. Yet the 

 whole is of post-tertiary origin, the fossil zoophj^tes and shells 

 being all of the same species as those now inhabiting the 

 neighboring sea.f In a calcareous conglomerate forming 

 part of the above-mentioned series of reefs, and supposed by 

 Agassiz, in accordance with his mode of estimating the rate 

 of growth of those reefs, to be about 10,000 years old, some 



* Dowler, cited by Dr. W. Usher, f Agassiz, in Nott and Gliddon, 



in Nott and Gliddon's Types of Man- ibid. p. 352. 

 kind, p. 352. 



