Sect. L THE GROWTH OF CORAL-REEFS. 
93 
an atoll of such large size,— and as the strip of land is for 
considerable spaces more than half a mile wide — also a 
very unusual circumstance, — we have the best possible 
evidence that Diego Garcia has remained at its present 
level for a very long period. With this fact, and with 
the knowledge that no sensible change has taken place 
during eighty years in the coral knolls, and considering 
that every single reef has reached the surface in other 
atolls, which do not present the smallest appearance of 
being older than Diego Garcia and Peros Banhos, and 
which are placed under the same external conditions 
with them, one is led to conclude that these submerged 
reefs, although covered with luxuriant coral, have no 
tendency to grow upwards, and that they would remain 
at their present levels for an indefinite period. 
From the number of these knolls, from their posi- 
tion, size, and form, — many of them being only one or 
two hundred yards across, with a rounded outline and 
precipitous sides,— it is indisputable that they have been 
formed by the growth of coral ; and this makes the case 
much more remarkable. In Peros Banhos and in the 
Great Chagos bank, some of these almost columnar 
masses are 200 feet high, and their summits lie only from 
two to eight fathoms beneath the surface ; therefore, 
a little greater proportional amount of growth would 
cause them to attain the surface, like those numerous 
knolls which rise from an equally great depth within 
the Maldiva atolls. We can hardly suppose that time 
has been wanting for the upward growth of the coral ; 
as in Diego Garcia, the broad annular strip of land, 
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