376 THE INHABITANTS OF THE SEA. 
for the great depths from which the coral-walls suddenly rise, 
and the annular form of lagoon islands. Yet this theory, in- 
genious as it was, could not stand the test of a closer examination: 
for no crater ever had such dimensions as, for instance, one of the 
Radack Islands, which is fifty-two miles long by twenty broad ; 
and no chain of mountains has its summits so equally high, as 
must have been the case with the numerous reef-bearing sub- 
marine rocks, considering the small depth from which the 
lithophytes build. Another seemingly inexplicable fact was, 
that, although corals hardly exist above low-water mark, reefs 
are found at Tongatabu or Eua, for instance, at elevations of 
forty and even three hundred feet above the level of the ocean. 
Mr. Charles Darwin was the first to give a satisfactory ex- 
planation of all the phenomena of coral formations, by ascribing 
them to the oscillations of the sea bottom, to its partial upheaving 
or subsidence. 
It is now perfectly well known that large portions of the 
continent of South America, Scandinavia, North Greenland, 
and many other coasts, are slowly rising, and that other ter- 
restrial or maritime areas are gradually subsiding. Thus 
on every side of the lagoon of the Keeling Islands, in which 
the water is as tranquil as in the most sheltered lake, Mr. 
Darwin saw old cocoa-nut trees undermined and falling. The 
foundation-posts of a storehouse on the beach, which, the in- 
habitants said, had stood seven years before just above high 
water, were now daily washed by the tide. 
Supposing on one of these subsiding areas an island-mountain 
fringed with corals, the lithophytes, keeping pace with the 
gradual sinking of their basis, soon raise again their solid 
masses to the level of the water; but not so with the land, each 
inch of whicb is irreclaimably gone. Thus the fringing reef 
will gradually become an encircling one ; and, if we suppose the 
sinking to continue, it must by the submergence of the central 
land, but upward growth of the ring of coral, be ultimately 
converted into a lagoon island. 
The numerous atolls of the Pacific and Indian Ocean give 
us a far insight into the past, and exhibit these seas overspread 
with lofty lands where there are now only humble monumental 
reefs dotted with verdant islets. Had there been no growing 
