FORMATION OF CORAL REEFS AND ISLANDS. 2353 
author has often witnessed this, and never saw reason to sup- 
pose that they clustered about the coral for any other purpose. 
It is an undoubted fact, as stated by Mr. Darwin, that frag- 
ments of coral and sand may be found in the stomachs of 
these animals, but this is not sufficient evidence of their 
browsing on thecoral. Fish so carefully avoid polyps of all 
kinds because of their power of stinging (as illustrated on 
p. 37), that we should wait for further and direct evidence 
on this point. The conclusion deduced by him from the facts, 
may be justly doubted. The fish and Holothurians, though 
numerous, are quite inadequate for the supply; and, more- 
over, we have, as explained above, an abundant source of the 
finest coral material without such aid. Motion of particle 
over particle will necessarily wear to dust, even though the 
particles be diamonds; and this incessant grinding action 
about reefs accounts satisfactorily for the deposits of coral 
mud, however great their extent. 
The coral world, as we thus perceive, is planted, like the 
land, with a variety of shrubs and smaller plants, and the el- 
ements and natural decay are producing gradual accumula- 
tions of material, like those of vegetation. The history of the 
growing reef has consequently its counterpart among the or- 
dinary occurrences of the land about us. 
The progress of the coral formation is like its commence- 
ment. The same causes continue, with similar results, and 
the reader might easily supply the details from the facts al- 
ready presented. The production of débris will necessarily 
continue to go on: a part will be swept by the waves, across 
the patch of reef, into the lagoon or channel beyond, while 
other portions will fill up the spaces among the corals along 
its margin, or be thrown beyond the margin and lodge on it- 
