And the only manner in which the reef could extend outwards, would
be by the gradual accumulation, at the foot of its seaward face, of a
talus of coral fragments torn off by the violence of the waves, which
talus might, in course of time, become high enough to bring its upper
surface within the limits of coral growth, and in that manner provide a
sort of factitious sea-bottom upon which the coral embryos might perch.
If, on the other hand, the level of the sea were slowly and gradually
lowered, it is clear that the parts of its bottom originally beyond the
limit of coral growth would gradually be brought within the required
distance of the surface, and thus the reef might be indefinitely
extended. But this process would give rise neither to an encircling reef
nor to an atoll, but to a broad belt of upheaved coral rock, increasing
the dimensions of the dry land, and continuous seawards with the fresh
fringing reef.
Suppose, however, that the sea-level rose instead of falling, at the
same slow and gradual rate at which we know it to be rising in some
parts of the world,--not more, in fact, than a few inches, or, at most,
a foot or two, in a hundred years. Then, while the reef would be unable
to extend itself seaward, the sea-bottom outside it being gradually more
and more removed from the depth at which the life of the coral polypes
is possible, it would be able to grow upwards as fast as the sea
rose.
Pages:
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197