MODE OF FORMATION. 107 
they would often be exterminated, were they not singularly tenacious 
of life, and ready to sprout anew on any rock where they may find 
quiet long enough to give themselves again a firm attachment. 
But it should be observed, that the sea would have far less effect 
upon the slender forms characterizing many zoophytes, among which 
the water finds free passage, than on the massive rock, against whose 
sides a large volume may drive unbroken. Moreover, much the 
greater part of the strength of the ocean is exerted near tide level, 
where it rises in breakers which plunge against the shores. Yet, 
owing to the many nooks and recesses deep among the corals, the 
rapidly moving waters, during the heavier swells, must produce whirl- 
ing eddies of considerable force, tending to uproot or break the coral 
clumps. These disrupting and transporting effects, will be less and 
less as we recede from the shores; yet all coral depths will experience 
them in some degree. 
There is another process going on over the coral field, somewhat 
analogous to vegetable decay, though still very different. Zoophytes 
have been described as ever dying while living. The dead portions 
are much smoothed down, or deprived of the roughening points which 
belong to the living coral, and the cells are sometimes half obliterated, 
or the delicate lamelle are worn away. ‘This may be viewed as one 
source of fine coral particles; and as the process is constantly going 
on, it is not an unimportant source. ‘This material is in a fit condi- 
tion to enter into solution, and it cannot be doubted that the water re- 
ceives lime from this source, which is afterwards yielded to the reef. 
In the Alcyonia family, which includes semi-fleshy corals, and the 
Gorgonie, the lime is often scattered through the polyps in granules ; 
and the process of death sets these calcareous grains free, which are 
consequently added to the coral sands. ‘The same process has been 
supposed to take place in the more common reef corals, the Madre- 
pores and Astreas, and it is possible that this may be to some extent 
the case. Yet it would seem, from facts observed, that after the secre- 
tion has begun, the secretion of lime going on takes place against the 
portions already formed, and in direct union with them, and not as 
granules to be afterwards cemented. 
The mud-lke deposits about coral reefs have been attributed to the 
causes just mentioned, but without due consideration. There is an 
unfailing and abundant source of this material in the self-triturating 
sands of the reefs acted upon by the moving waters. On the seaward 
side of coral islands, and on the shores of the larger lagoons, where 
