108 CORAL FORMATIONS. 
the surface rises into waves of much magnitude, the finer portions are 
carried off, and the coarser sand alone remains to form the beaches. 
This is a well-known fact common on all shores exposed to the waves, 
coral or not coral, and to this cause the sandy character is attributed. 
But in the smaller lagoons, where the water is only rippled by the 
winds, or roughened for short intervals, the trituration is of the 
gentlest kind possible, and, moreover, the finely pulverized material 
remains as part of the shores. ‘Thus the fine material of the mud 
must be constantly forming, on all the shores, for the sands are per- 
petually wearing themselves out; but the mud accumulates only in 
the more quiet waters, and within the lagoons and channels, where it 
settles, after being washed out from the beaches. ‘This corresponds 
exactly with the facts; and every lake and pool of water of our conti- 
nents illustrates the same point.* 
The coral world, as we thus perceive, is planted, like the land, 
with a variety of shrubs and smaller plants, and: the elements and 
natural decay are producing gradual accumulations of material, like 
those of vegetation. The history of the growing reef has consequently 
its counterpart among the ordinary occurrences of the land about us. 
The progress of the coral formation is like itscommencement. The 
same causes continue with similar results, and the reader might 
easily supply the details from the facts already presented. ‘T'he pro- 
duction of debris will necessarily continue to go on; a part will be 
* Mr. Darwin, in discussing the origin of the finer calcareous mud, (op. cit. p. 14), 
supposes that it is derived, in part, from fishes and Holothurias, and other authors have 
thrown out the same suggestion. He cites as a fact, on the authority of Mr. Liesk, 
that certain fish browse on the living zoophytes; and from Mr. Allan, of Forres, he 
learned also that Holothurias subsisted on them. With regard to the facts here stated, I 
can make no definite assertion. Small fish swarm about the branching clumps, and when 
disturbed, seek shelter at once among the branches, where they are safe from pursuit. 
I have often witnessed this fact, and never saw reason to suppose that they clustered 
about the coral for any other purpose, It is an undoubted fact, however, as stated by 
Mr. Darwin, that fragments of coral and sand may be found in the stomachs of these 
animals, though this is no evidence of their browsing on the coral. The conclusion 
deduced by him from the facts may be justly doubted. The fish and Holothurias, though 
numerous, are quite inadequate for the supply ; and, moreover, we have, as explained 
above, an abundant source of the finest coral material without such aid. Motion of par- 
ticle 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 large they may be. 
