NOTES ON THE GEOLOGY OF THE BAHAMAS 45 



Providence and Andros, have very recently been rising; and yet, 

 although I have no measurements, I venture to state that Salt Cay, the 

 most seaward one, is as high if not higher than Hog Island, that lies 

 inside of it. 



To return to Florida. It would seem at first as if the conclusions of 

 Professor Heilprin precluded the possibility of the cays being formed 

 as suggested by Agassiz ; for if we suppose a cay to be formed while the 

 land is rising, and then that another forms to seaward, and this process 

 to continue until three or four cays were formed one outside of the 

 other, it seems as if the first one would be higher above the level of the 

 sea than the last, and this Agassiz "■ states is not the case. When I first 

 read Agassiz's memoir I was much impressed with the strength of his 

 arguments. But Heilprin's in regard to elevation are conclusive ; and 

 although he did not visit the lower part of the peninsula, it is probable 

 that its movement is in the same direction as that portion examined. 



It will, however, be noticed that Agassiz lays no stress on the effects 

 of the erosion that takes place so rapidly on all islands of coral forma- 

 tion. 



I believe that the views of these two eminent observers can be 

 brought into harmony by considering the effects of erosion. Let us . 

 suppose a cay has been formed of calcareous material thrown up by the 

 waves to a height of fifteen or twenty feet. Then, while the cay to 

 seaward was being formed, the erosion would take place on the one 

 already made, and whether its height above the sea increased, remained 

 constant, or decreased would depend upon the relative effects of the 

 elevation and erosion. It is not improbable that these two forces might 

 balance each other ; and if this were so, it is easy to show diagrammati- 

 cally that any number of cays could form, one after the other, to sea- 

 ward, and yet the first be no higher than the last above the level of the 

 sea. And this argument also applies to the cays near Nassau. It is 

 probable that the ocean would throw up some of the cays higher than 

 the others, and also that a slight difference in height would not be 

 observed by the unaided eye. 



• "Report, on Florida Reefs," Mem. Mus. Comp. Zool., Vol. VII, No. i, p. 36. 



