282 ALEXANDER AGASSIZ 



tracing" the growth of the reefs and the formation of 

 the Peninsula, I have come across no signs of any eleva- 

 tion. Everything, on the contrary, tends to show that the 

 immense plateau which forms the base upon which the 

 Peninsula of Florida is formed, was built up by the debris 

 of animal remains, — Mollusks, Corals, Echinoderms, 

 etc. (after it had originally reached a certain depth in 

 the ocean), until it reached the proper height for corals 

 to flourish. This here is not much deeper than seven 

 to eight fathoms ; generally six fathoms marks the limit. 

 To the westward of this group of reefs is a coral reef 

 starting on a bank at a depth of seven fathoms. 



I expect to publish a small map of the distribution of 

 the corals of the Tortugas as soon as I return home, in 

 my report of work (not done) to the Superintendent of 

 the Coast Survey. I shall, however, have first to finish 

 reading the proofs of the Challenger Echini, the last 

 pages of which I expect to find awaiting my return 

 home, and I trust you will see that Memoir out during 

 the summer. 



To this Darwin replied in a letter characteristically 

 full of courtesy and open-mindedness, qualities not 

 always conspicuous in scientific discussions. It has al- 

 ready been published in " More Letters of Charles Dar- 

 win," but a few passages may not be out of place 

 here : — 



"You will have seen Mr. Murray's views on the 

 formation of atolls and barrier reefs. Before publishing 

 my book I thought long over the same view, but only 

 as far as ordinary marine organisms are concerned, for 

 at that time little was known of the multitude of miu- 



