FORMATION OF* CORAL REEFS. 171 
obtain a view of them in this state, for, at any 
approach, they draw themselves in, and remain 
closed to all investigation. Only once, for a 
short hour, I had this opportunity ; during that 
time one of these little creatures revealed to me 
its whole structure, as if to tell me, once for all, 
the story of its existence through all the succes- 
sive epochs from the dawn of Creation till now, 
and then withdrew. With my most patient 
watching, I have never been able to see one of 
them open again. But to establish the fact that 
one of the Corals represented from the earliest 
period, and indeed far more numerous in the 
beginning than any other, was in truth no 
Polyp, but an Acaleph, the glimpse I had was 
all-sufficient. It came out as if to bear witness 
of its class, — as if to say, ‘* We, too, were 
among the hosts of living beings with which 
God first peopled his earth.” 
With these branching Corals the reef reaches 
the level of high-water, beyond which, as I have 
said, there can be no further growth, for want of 
the action of the fresh sea-water. This depend- 
ence upon the vivifying influence of the sea ac- 
counts for one unfailing feature in the Coral 
walls. They are always abrupt and steep on the 
seaward side, but have a gentle slope towards the 
land. This is accounted for by the circum- 
stance that the Corals on the outer side of the 
