THE CORAL-REEF PROBLEM. 61 



cumulations, whose present positions, whether of horizontal or 

 vertical distribution, have practically no connection with re- 

 cent movements either of elevation or depression. " There is 

 practically no evidence that the Florida reef, or any part of the 

 southern peninsula of Florida which has been formed by corals, 

 owes its existence to the effect of elevation ; or that the atolls of 

 this district, such as those of the Marquesas or of the great 

 Alacran Reef, owe their peculiar structure to subsidence.'" On. 

 what evidence, it might be asked, rest these assertions ? It may 

 not be easy to prove subsidence in the case of the Marquesas 

 and the Alacran Reef, but I believe it would be equally diffi- 

 cult to prove the reverse proposition — i. e., that there has been no 

 subsidence. As far as the Florida reefs themselves are concerned, 

 I believe the evidence is all but conclusive that they owe much, 

 if not most, of their existence to uplift, and to uplift within a 

 recent geological period. My own researches in the southern 

 part of the peninsula have demonstrated the existence of Plio- 

 cene deposits in vast horizontal, or nearly horizontal, beds as far 

 south as the Caloosahatchie, and there can be no question that 

 these deposits, which rise to 10 or 15 feet above thelevel of the sea, 

 are continued for some distance still further to the south.'' The 

 same deposits, moreover, are capped by deposits of Post-Pliocene 

 age, proving that an uplift took place in this region as late as the 

 Post-Pliocene period. That this uplift should not have affected 

 the apex of the peninsula, and even the reefs beyond, seems 

 scarcely credible. From what we now know of the structure of 

 the Floridian peninsula it is clear that this portion of the 

 North American continent represents a comparatively old 

 chapter in geological history, and that it has passed through 

 much the same phases of construction as the border area of the 

 Eastern and Southern United States. Its periods of elevation 

 and depression, extending back through the greater portion of 

 the Tertiarj'^ epoch, were largely coincident with those of the 



1" Three Cruises of the Blake." I, p. 61 . 1888. 



^" Explorations on the West Coast of Florida and in the (Dkeechobee Wilder- 

 ness," 1887. 



