486 LOUIS AGASSIZ. 



I shall send you as soon as it is printed. The 

 case is this. There are several concentric 

 reefs separated by deep channels ; the penin- 

 sula of Florida itself is a succession of such 

 reefs, the everglades being the filled-up chan- 

 nels, while the hummocks were formerly little 

 intervening islands, like the mangrove islands 

 in the present channels. But what is quite 

 remarkable, all these concentric reefs are upon 

 one level, above that of the sea, and there is 

 no indication whatever of upheaval. You will 

 find some observations upon upheavals, etc., 

 in Silliman, by Tuomey ; it is a great mistake, 

 as I shall show. The Tortugas are a real 

 atoll, but formed without the remotest indi- 

 cation of subsidence. 



Of course this does not interfere in the 

 least with the views of Darwin, for the whole 

 ground presents peculiar features. I wish 

 you would tell him something about this. 

 One of the most remarkable peculiarities of 

 the rocks in the reefs of the Tortugas consists 

 in their composition ; they are chiefly made 

 up of Corallines, limestone algae, and, to a 

 small extent only, of real corals. . . . 



Agassiz's report to the Coast Survey upon 

 the results of this first investigation made by 



