44 COKAL REEFS OF FLORIDA. CHAP. III. 



1846, 1 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 geo 

 logist enjoy a more favourable opportunity for estimating in 

 years the duration of certain portions of the recent epoch.* 



Coral Reefs 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 activity, 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 zoophytes and shells 

 being all of the same species as those now inhabiting the 

 neighbouring 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 G-liddon, 



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

 kind, p. 352. 



