284 ALEXANDER AGASSIZ 



than they accumulated on the hottom. This would also 

 be the case in shallow water, where a thin layer of 

 pelagic life would uot furnish so many shells. At inter- 

 mediate depths, on the other hand, the shells, having 

 less distance to fall, would be less dissolved, and would 

 accumulate. 



TO DARWIN 



Cambridge, May 19, 1881. 



I find on my return from the Tortugas your most 

 welcome letter of May 5. I am now at work on the Re- 

 port of the Coral Reefs of the Tortugas, and hope dur- 

 ing the course of the summer to be able to send it to 

 you. As you well say, the fact that the Peninsula of 

 Florida should have remained at the same level for so 

 long a time is most surprising. This I consider to be in 

 part due to the original orographic conditions of the 

 Gulf of Mexico, as we have not only the Florida Penin- 

 sula but other equally important banks : Yucatan, Ba- 

 hamas, and San Pedro Banks, all of which are character- 

 ized by a general dead level which they have evidently 

 kept for an immense period of time. Yet on the other 

 side of the Straits of Florida and all along 1 the line of 

 the larger Antilles, as far as Barbados, and along the 

 northern of the Windward Islands, we have the most 

 distinct proof of elevation. . . . 



I should feel at present inclined to assign to the action 

 of large marine animals (such as Gorgonise, Starfisbes, 

 Mollusks, Echinoderms, Deep-sea Corals, Crustacea, etc.) 

 a more important part in building up a plateau, up to 

 the height at which corals can thrive, than to the pelagic 

 fauna which I would look upon more as the cementing 

 medium, but which, however, in some localities, such as 



