132 



THE TORTUGAS AND FLORIDA REEFS. 



ds the north, as far as the temperature would 



pply of food far more 



abundant than that with which the fauna of the eastern coast was supplied before 



ch a break of continuity existed 



As 



separation of the Atlantic and Pacifi 



probably took place late in the Cretaceous period, and was perhaps not completed 

 till the Middle Tertiary, we shall naturally expect to find the marine fauna of the 

 earlier geological periods of the Old and the New World to be very similar, and con- 



sisting of many identical 



species 



These older faunas flourished on the shores and 



continental shelves, either washed by the great equatorial currents or by branches 

 extending both north and south along the then existing continents and continental 



islands ; 

 the beds 



d 



fi 



r 



fossilifer 



deposits 



the time of their formation lay in the 



we may feel assured that 

 of a primary or a secon- 



dary marine current, which supplied an abundance of pelagic food indirectly necessary 

 for the support of any rich marine fauna. 



