and either gives
way and lets it come through, or else is raised up by its violence. And
so Mr. Darwin, being desirous not to merely put out a flashy hypothesis,
but to get at the truth of the matter, said to himself, "If my notion of
this matter is right, then atolls and encircling reefs, inasmuch as they
are dependent upon subsidence, ought not to be found in company with
volcanoes; and, 'vice versa', volcanoes ought not to be found in company
with atolls, but they ought to be found in company with fringing reefs."
And if you turn to Mr. Darwin's great work upon the coral reefs, you
will see a very beautiful chart of the world, which he prepared with
great pains and labour, showing the distribution on the one hand of the
reefs, and on the other of the volcanoes; you will find that in no case
does the atoll accompany the volcano, or the volcano burst up among the
atolls. It is most instructive to look at the great area of the Pacific
on the map, and see the great masses of atolls forming in one region of
it a most enormous belt, running from north-west to south-east; while
the volcanoes, which are very numerous in that region, go round the
margin, so that we can picture the Pacific to ourselves a section of a
kind of very shallow basin--shallow in proportion to its width, with the
atolls rising from the bottom of it, and at the margins the volcanoes.
It is exactly as if you had taken a flat mass and lifted up the edges
of it; the subterranean force which lifted up the edges shows itself
in volcanoes, and as the edges have been raised, the middle part of
the mass has gone down. In other words, the facts of physical geography
precisely and exactly correspond with the hypothesis which accounts for
the infinite varieties of coral reefs.

One other point, before I conclude, about this matter. These reefs, as
you have just perceived, are in a most singular and unexpected manner
indications of physical changes of elevations and depressions going on
upon the surface of the globe. I dare say it may have surprised you to
hear me talk in this familiar sort of way of land going up and down;
but it is one of the universal lessons of geology that the land is
going down and going up, and has been going up and down, in all sorts
of places and to all sorts of distances, through all recorded time.
Geologists would be quite right in maintaining the seeming paradox that
the stable thing in the world is the fluid sea and the shifting thing