improbable: such a chain of mountains was never known.
Then how can you possibly account for the curious circular form of the
atolls by any supposition of this kind? I believe there was some one who
imagined that all these mountains were volcanoes, and that the reefs
had grown round the tops of the craters, so we all stuck fast. I may say
"we," though it was rather before my time. And when we all stick fast,
it is just the use of a man of genius that he comes and shows us the
meaning of the thing. He generally gives an explanation which is so
ridiculously simple that everybody is ashamed that he did not find
it out before; and the way such a discoverer is often rewarded is by
finding out that some one had made the discovery before him! I do not
mean to say that it was so in this particular instance, because the
great man who played the part of Columbus and the egg on this occasion
had, I believe, always had the full credit which he so well deserves.
The discoverer of the key to these problems was a man whose name you
know very well in connection with other matters, and I should not wonder
if some of you have heard it said that he was a superficial kind of
person who did not know much about the subject on which he writes. He
was Mr. Darwin, and this brilliant discovery of his was made public
thirty years ago, long before he became the celebrated man he now
is; and it was one of the most singular instances of that astonishing
sagacity which he possesses of drawing consequences by way of deduction
from simple principles of natural science--a power which has served him
in good stead on other occasions. Well, Mr. Darwin, looking at these
curious difficulties and having that sort of knowledge of natural
phenomena in general, without which he could not have made a step
towards the solution of the problem, said to himself--"It is perfectly
clear that the coral which forms the base of the atolls and fringing
reefs could not possibly have been formed there if the level of the sea
has always been exactly where it is now, for we know for certain that
these polypes cannot build at a greater depth than 20 to 25 fathoms, and
here we find them at 50 to 100 fathoms."

That was the first point to make clear. The second point to deal with
was--if the polypes cannot have built there while the level of the
sea has remained stationary, then one of two things must have
happened--either the sea has gone up, or the land has gone down.

There i