184 AGE OF CORAL REEFS. 



Some of my readers may ask why the Reef 

 does not rise evenly to the level of the sea, and 

 form a continuous line of land, instead of here 

 and there an island. This is accounted for by 

 the sensitiveness of the Corals to any unfavorable 

 circumstances impeding their growth, as well as 

 by the different rates of increase of their differ- 

 ent kinds. Wherever any current from the shore 

 flows over the Reef, bringing with it impurities 

 from the land, there the growth of the Corals 

 will be less rapid, and consequently that portion 

 of the Reef will not reach the surface so soon 

 as other parts, where no such unfavorable influ- 

 ences have interrupted the growth. But in the 

 course of time the outer Reef will reach the 

 surface for its whole length, and become united 

 to the inner one by the filling up of the channel 

 between them, while the inner one will long 

 before that time become solidly united to the 

 present shore-bluffs of Florida by the consolida- 

 tion of the mud-flats, which will one day trans- 

 form the inner channel 'into dry land. 



What is now the rate of growth of these Coral 

 Reefs ? We cannot, perhaps, estimate it with 

 absolute accuracy, since they are now so nearly 

 completed ; but Coral growth is constantly spring- 

 ing up wherever it can find a foothold, and it 

 is not difficult to ascertain approximately the 

 rate of growth of the different kinds. Even this, 



