652 LOUIS AGASSIZ. 



indispensable to the completion of the work. 

 The reef is formed mainly by the accumula- 

 tion of solid materials from a variety of ani- 

 mals and a few plants. The relations of 

 these animals and plants to one another while 

 alive, in and upon the reef, ought to be stud- 

 ied more fully than has been the case here- 

 tofore, in order to determine with certainty 

 the share they have in the formation of these 

 immense submarine walls so dangerous to 

 navigation. The surveys, as they have been 

 made thus far, furnish only the necessary in- 

 formation concerning the present form and 

 extent of the reef. But we know that it is 

 constantly changing, increasing, enlarging, 

 spreading, rising in such a way and at such a 

 rate, that the surveys of one century become 

 insufficient for the next. A knowledge of 

 these changes can only be obtained by a nal 

 uralist, familiar with the structure and mod( 

 of growth of the animals. The survey I made 

 about fifteen years ago, at the request of your 

 lamented predecessor, could only be consid- 

 ered as a reconnaissance, in view of the ex- 

 tent and importance of the work. I would, 

 therefore, recommend you to organize a party 

 specially detailed to carry on these investiga- 

 tions in connection with, and by the side of, 



