explanation of this kind simply because it explained one particular set
of facts。 Before you can possibly be safe in dealing with Naturewho
is very properly made of the feminine gender； on account of the
astonishing tricks which she plays upon her admirers！I say before you
can be safe in dealing with Nature； you must get two or three kinds of
cross proofs； so as to make sure not only that your hypothesis fits
that particular set of facts； but that it is not contradicted by some
other set of facts which is just as clear and certain。 And it so
happens； that in this case Mr。 Darwin supplied the cross proofs as well
as the immediate evidence。 You have all heard of volcanoes； those
wonderful vents in the surface of the earth out of which pour masses of
lava； cinders and ashes； and the like。 Now； it is a matter of
observation and experience that all volcanoes are placed in areas in
which the surface of the earth is undergoing elevation； or at any rate
is stationary； they are not placed in parts of the world in which the
level of the land is being lowered。 They are all indications of a
great subterranean activity； of a something being pushed up； and
therefore naturally the land 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 basinshallow 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
is the solid land。 That may sound a very hard saying at first； but the
more you look into geology； the more you will see ground for believing
that it is not a mere paradox。
In an unexpected manner； again； these reefs afford us not only an
indication of change of place； but they afford an indication of lapse
of time。 The reef is a timekeeper of a very curious character； and you
can easily understand why。 The coral polype； like everything else；
takes a certain time to grow to its full size； it does not do it in a
minute； just as a child takes a certain time to grow into a man so does
the embryo polype take time to grow into a perfect polype and form its
skeleton。 Consequently every particle of coral limestone is an
expression of time。 It must have taken a certain time to separate the
lime from the sea water。 It is not possible to arrive at an accurate
computation of the time it must have taken to form these coral islands；
because we lack the necessary data； but we can form a rough calculation；
which leads to very curious and striking results。 The computations of
the rate at which corals grow are so exceedingly variable； that we must
allow the widest possible margin for error； and it is better in this
case to make the allowance upon the side of excess。 I think that
anybody who knows anything about the matter will tell you that I am
making a computation far in excess of what is probable； if I say that
an inch of coral limestone may be added to one of these reefs in the
course of a year。 I think most naturalists would be inclined to laugh
at me for making such an assumption； and would put the growth at
certainly not more than half that amount。 But supposing it is so； what
a very curious notion of the antiquity of some of these great living
pyramids comes out by a very simple calculation。 There is no doubt
whatever that the sea faces of some of them are fully a thousand feet
high； and if you take the reckoning of an inch a year； that will give
you 12；000 years for the age of that particular pyramid or cone of
coral limestone； 12；000 long years have these creatures been labouring
in conditions which must have been substantially the same as they are
now； otherwise the polypes could not have continued their work。 But I
believe I very much understate both the height of some of these masses；
and overstate the amount which these animals can form in the course of a
year； so that you might very safely double the period as the time
during which the Pacific Ocean； the general state of the climate； and
the sea； and the temperature has been substantially what it is now； and
yet that state of things which now obtains in the Pacific Ocean is the
yesterday of the history of the life of the globe。 Those pyramids of
coral rock are built upon a foundation which is itself formed by the
deposits which the geologist has to deal with。 If we go back in time
and search through the series of the rocks； we find at every age of the
world's history which has yet been examined； accumulations of
limestone； many of which have certainly been built up in just the same
way as those coral reefs which are now forming the bottom of the
Pacific Ocean。 And even if we turn to the oldest periods of geologic
history； although the nature of the materials is changed； although we
cannot apply to them the same reasonings that we can to the existing
corals； yet still there are vast masses of limestone formed of nothing
else than the accumulations of the skeletons of similar animals； and
testifying that even in those remote periods of the world's history； as
now； the order of things implies that the earth had already endured for
a period of which our ordinary standards of chronology give us not the
slightest conception。 In other words； the history of these coral reefs；
traced out honestly and carefully； and with the same sort of reasoning
that you would use in the ordinary affairs of life； testifies； like
every fact that I know of； to the prodigious antiquity of the earth
since it existed in a condition in the main similar to that in which it
now is。
End