Critical introduction by John W. Judd

THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS.


CRITICAL INTRODUCTION.

A scientific discovery is the outcome of an interesting process of
evolution in the mind of its author.  When we are able to detect the germs
of thought in which such a discovery has originated, and to trace the
successive stages of the reasoning by which the crude idea has developed
into an epoch-making book, we have the materials for reconstructing an
important chapter of scientific history.  Such a contribution to the story
of the "making of science" may be furnished in respect to Darwin's famous
theory of coral-reefs, and the clearly reasoned treatise in which it was
first fully set forth.

The subject of corals and coral-reefs is one concerning which much popular
misconception has always prevailed.  The misleading comparison of coral-rock
with the combs of bees and the nests of wasps is perhaps responsible
for much of this misunderstanding; one writer has indeed described a
coral-reef as being "built by fishes by means of their teeth."  Scarcely
less misleading, however, are the references we so frequently meet with,
both in prose and verse, to the "skill," "industry," and "perseverance" of
the "coral-insect" in "building" his "home."  As well might we praise men
for their cleverness in making their own skeletons, and laud their assiduity
in filling churchyards with the same.  The polyps and other organisms, whose
remains accumulate to form a coral-reef, simply live and perform their
natural functions, and then die, leaving behind them, in the natural course
of events, the hard calcareous portions of their structures to add to the
growing reef.

While the forms of coral-reefs and coral-islands are sometimes very
remarkable and worthy of attentive study, there is no ground, it need
scarcely be added, for the suggestion that they afford proofs of design on
the part of the living builders, or that, in the words of Flinders, they
constitute breastworks, defending the workshops from whence "infant
colonies might be safely sent forth."

It was not till the beginning of the present century that travellers like
Beechey, Chamisso, Quoy and Gaimard, Moresby, Nelson, and others, began to
collect accurate details concerning the forms and structure of coral-masses,
and to make such observations on the habits of reef-forming polyps,
as might serve as a basis for safe reasoning concerning the origin of
coral-reefs and islands.  In the second volume of Lyell's "Principles of
Geology," published in 1832, the final chapter gives an admirable summary
of all that was then known on the subject.  At that time, the ring-form of
the atolls was almost universally regarded as a proof that they had grown
up on submerged volcanic craters; and Lyell gave his powerful support to
that theory.

Charles Darwin was never tired of acknowledging his indebtedness to Lyell.
In dedicating to his friend the second edition of his "Naturalist's Voyage
Round the World," Darwin writes that he does so "with grateful pleasure, as
an acknowledgment that the chief part of whatever scientific merit this
journal and the other works of the author may possess, has been derived
from studying the well-known and admirable 'Principles of Geology.'"

The second volume of Lyell's "Principles" appeared after Darwin had left
England; but it was doubtless sent on to him without delay by his faithful
friend and correspondent, Professor Henslow.  It appears to have reached
Darwin at a most opportune moment, while, in fact, he was studying the
striking evidences of slow and long-continued, but often interrupted
movement on the west coast of South America.  Darwin's acute mind could not
fail to detect the weakness of the then prevalent theory concerning the
origin of the ring-shaped atolls--and the difficulty which he found in
accepting the volcanic theory, as an explanation of the phenomena of
coral-reefs, is well set forth in his book.

In an interesting fragment of autobiography, Darwin has given us a very
clear account of the way in which the leading idea of the theory of
coral-reefs originated in his mind; he writes, "No other work of mine was
begun in so deductive a spirit as this, for the whole theory was thought
out on the west coast of South America, before I had seen a true
coral-reef.  I had therefore only to verify and extend my views by a
careful examination of living reefs.  But it should be observed that I had
during the two previous years been incessantly attending to the effects on
the shores of South America of the intermittent elevation of the land,
together with the denudation and deposition of sediment.  This necessarily
led me to reflect much on the effects of subsidence, and it was easy to
replace in imagination the continued deposition of sediment by the upward
growth of corals.  To do this was to form my theory of the formation of
barrier-reefs and atolls."

On her homeward voyage, the "Beagle" visited Tahiti, Australia, and some of
the coral-islands in the Indian Ocean, and Darwin had an opportunity of
testing and verifying the conclusion at which he had arrived by studying
the statements of other observers.

I well recollect a remarkable conversation I had with Darwin, shortly after
the death of Lyell.  With characteristic modesty, he told me that he never
fully realised the importance of his theory of coral-reefs till he had an
opportunity of discussing it with Lyell, shortly after the return of the
"Beagle".  Lyell, on receiving from the lips of its author a sketch of the
new theory, was so overcome with delight that he danced about and threw
himself into the wildest contortions, as was his manner when excessively
pleased.  He wrote shortly afterwards to Darwin as follows:--"I could think
of nothing for days after your lesson on coral-reefs, but of the tops of
submerged continents.  It is all true, but do not flatter yourself that you
will be believed till you are growing bald like me, with hard work and
vexation at the incredulity of the world."  On May 24th, 1837, Lyell wrote
to Sir John Herschel as follows:--"I am very full of Darwin's new theory of
coral-islands, and have urged Whewell to make him read it at our next
meeting.  I must give up my volcanic crater forever, though it cost me a
pang at first, for it accounted for so much."  Dr. Whewell was president of
the Geological Society at the time, and on May 31st, 1837, Darwin read a
paper entitled "On Certain Areas of Elevation and Subsidence in the Pacific
and Indian oceans, as deduced from the Study of Coral Formations," an
abstract of which appeared in the second volume of the Society's
proceedings.

It was about this time that Darwin, having settled himself in lodgings at
Great Marlborough Street, commenced the writing of his book on "Coral-Reefs."
Many delays from ill-health and the interruption of other work,
caused the progress to be slow, and his journal speaks of "recommencing"
the subject in February 1839, shortly after his marriage, and again in
October of the same year.  In July 1841, he states that he began once more
"after more than thirteen month's interval," and the last proof-sheet of
the book was not corrected till May 6th, 1842.  Darwin writes in his
autobiography, "This book, though a small one, cost me twenty months of
hard work, as I had to read every work on the islands of the Pacific, and
to consult many charts."  The task of elaborating and writing out his books
was, with Darwin, always a very slow and laborious one; but it is clear
that in accomplishing the work now under consideration, there was a long
and constant struggle with the lethargy and weakness resulting from the sad
condition of his health at that time.

Lyell's anticipation that the theory of coral-reefs would be slow in
meeting with general acceptance was certainly not justified by the actual
facts.  On the contrary the new book was at once received with general
assent among both geologists and zoologists, and even attracted a
considerable amount of attention from the general public.

It was not long before the coral-reef theory of Darwin found an able
exponent and sturdy champion in the person of the great American
naturalist, Professor James D. Dana.  Two years after the return of the
"Beagle" to England, the ships of the United States Exploring Expedition
set sail upon their four years' cruise, under the command of Captain
Wilkes, and Dana was a member of the scientific staff.  When, in 1839, the
expedition arrived at Sydney, a newspaper paragraph was found which gave
the American naturalist the first intimation of Darwin's new theory of the
origin of atolls and barrier-reefs.  Writing in 1872, Dana describes the
effect produced on his mind by reading this passage:--"The paragraph threw
a flood of light over the subject, and called forth feelings of peculiar
satisfaction, and of gratefulness to Mr. Darwin, which still come up afresh
whenever the subject of coral islands is mentioned.  The Gambier Islands in
the Paumotus, which gave him the key to the theory, I had not seen; but on
reaching the Feejees, six months later, in 1840, I found there similar
facts on a still grander scale and of a more diversified character, so that
I was afterward enabled to speak of his theory as established with more
positiveness than he himself, in his philosophic caution, had been ready to
adopt.  His work on coral-reefs appeared in 1842, when my report on the
subject was already in manuscript.  It showed that the conclusions on other
points, which we had independently reached, were for the most part the
same.  The principal points of difference relate to the reason for the
absence of corals from some coasts, and the evidence therefrom as to
changes of level, and the distribution of the oceanic regions of elevation
and subsidence--topics which a wide range of travel over the Pacific
brought directly and constantly to my attention."

Among the Reports of the United States Exploring Expedition, two important
works from the pen of Professor Dana made their appearance;--one on
"Zoophytes," which treats at length on "Corals and Coral-Animals," and the
other on "Coral-Reefs and Islands."  In 1872, Dana prepared a work of a
more popular character in which some of the chief results of his studies
are described; it bore the title of "Corals and Coral-Islands."  Of this
work, new and enlarged editions appeared in 1874 and 1890 in America, while
two editions were published in this country in 1872 and 1875.  In all these
works their author, while maintaining an independent judgment on certain
matters of detail, warmly defends the views of Darwin on all points
essential to the theory.

Another able exponent and illustrator of the theory of coral-reefs was
found in Professor J.B. Jukes, who accompanied H.M.S. "Fly", as naturalist,
during the survey of the Great Barrier-Reef--in the years 1842 to 1846.
Jukes, who was a man of great acuteness as well as independence of mind,
concludes his account of the great Australian reefs with the following
words:--"After seeing much of the Great Barrier-Reefs, and reflecting much
upon them, and trying if it were possible by any means to evade the
conclusions to which Mr. Darwin has come, I cannot help adding that his
hypothesis is perfectly satisfactory to my mind, and rises beyond a mere
hypothesis into the true theory of coral-reefs."

As the result of the clear exposition of the subject by Darwin, Lyell,
Dana, and Jukes, the theory of coral-reefs had, by the middle of the
present century, commanded the almost universal assent of both biologists
and geologists.  In 1859 Baron von Richthofen brought forward new facts in
its support, by showing that the existence of the thick masses of dolomitic
limestone in the Tyrol could be best accounted for if they were regarded as
of coralline origin and as being formed during a period of long continued
subsidence.  The same views were maintained by Professor Mojsisovics in his
"Dolomit-riffe von Sudtirol und Venetien," which appeared in 1879.

The first serious note of dissent to the generally accepted theory was
heard in 1863, when a distinguished German naturalist, Dr. Karl Semper,
declared that his study of the Pelew Islands showed that uninterrupted
subsidence could not have been going on in that region.  Dr. Semper's
objections were very carefully considered by Mr. Darwin, and a reply to
them appeared in the second and revised edition of his "Coral-Reefs," which
was published in 1874.  With characteristic frankness and freedom from
prejudice, Darwin admitted that the facts brought forward by Dr. Semper
proved that in certain specified cases, subsidence could not have played
the chief part in originating the peculiar forms of the coral-islands.  But
while making this admission, he firmly maintained that exceptional cases,
like those described in the Pelew Islands, were not sufficient to
invalidate the theory of subsidence as applied to the widely spread atolls,
encircling reefs, and barrier-reefs of the Pacific and Indian Oceans.  It
is worthy of note that to the end of his life Darwin maintained a friendly
correspondence with Semper concerning the points on which they were at
issue.

After the appearance of Semper's work, Dr. J.J. Rein published an account
of the Bermudas, in which he opposed the interpretation of the structure of
the islands given by Nelson and other authors, and maintained that the
facts observed in them are opposed to the views of Darwin.  Although, so
far as I am aware, Darwin had no opportunity of studying and considering
these particular objections, it may be mentioned that two American
geologists have since carefully re-examined the district--Professor W.N.
Rice in 1884 and Professor A. Heilprin in 1889--and they have independently
arrived at the conclusion that Dr. Rein's objections cannot be maintained.

The most serious opposition to Darwin's coral-reef theory, however, was
that which developed itself after the return of H.M.S. "Challenger" from
her famous voyage.  Mr. John Murray, one of the staff of naturalists on
board that vessel, propounded a new theory of coral-reefs, and maintained
that the view that they were formed by subsidence was one that was no
longer tenable; these objections have been supported by Professor Alexander
Agassiz in the United States, and by Dr. A. Geikie, and Dr. H.B. Guppy in
this country.

Although Mr. Darwin did not live to bring out a third edition of his
"Coral-Reefs," I know from several conversations with him that he had given
the most patient and thoughtful consideration to Mr. Murray's paper on the
subject.  He admitted to me that had he known, when he wrote his work, of
the abundant deposition of the remains of calcareous organisms on the sea
floor, he might have regarded this cause as sufficient in a few cases to
raise the summits of submerged volcanoes or other mountains to a level at
which reef-forming corals can commence to flourish.  But he did not think
that the admission that under certain favourable conditions, atolls might
be thus formed without subsidence, necessitated an abandonment of his
theory in the case of the innumerable examples of the kind which stud the
Indian and Pacific Oceans.

A letter written by Darwin to Professor Alexander Agassiz in May 1881 shows
exactly the attitude which careful consideration of the subject led him to
maintain towards the theory propounded by Mr. Murray:--"You will have
seen," he writes, "Mr. Murray's views on the formation of atolls and
barrier-reefs.  Before publishing my book, I thought long over the same
view, but only as far as ordinary marine organisms are concerned, for at
that time little was known of the multitude of minute oceanic organisms.  I
rejected this view, as from the few dredgings made in the "Beagle", in the
south temperate regions, I concluded that shells, the smaller corals, etc.,
decayed and were dissolved when not protected by the deposition of
sediment, and sediment could not accumulate in the open ocean.  Certainly,
shells, etc., were in several cases completely rotten, and crumbled into
mud between my fingers; but you will know whether this is in any degree
common.  I have expressly said that a bank at the proper depth would give
rise to an atoll, which could not be distinguished from one formed during
subsidence.  I can, however, hardly believe in the existence of as many
banks (there having been no subsidence) as there are atolls in the great
oceans, within a reasonable depth, on which minute oceanic organisms could
have accumulated to the depth of many hundred feet."

Darwin's concluding words in the same letter written within a year of his
death, are a striking proof of the candour and openness of mind which he
preserved so well to the end, in this as in other controversies.

"If I am wrong, the sooner I am knocked on the head and annihilated so much
the better.  It still seems to me a marvellous thing that there should not
have been much, and long-continued, subsidence in the beds of the great
oceans.  I wish some doubly rich millionaire would take it into his head to
have borings made in some of the Pacific and Indian atolls, and bring home
cores for slicing from a depth of 500 or 600 feet."

It is noteworthy that the objections to Darwin's theory have for the most
part proceeded from zoologists, while those who have fully appreciated the
geological aspect of the question, have been the staunchest supporters of
the theory of subsidence.  The desirability of such boring operations in
atolls has been insisted upon by several geologists, and it may be hoped
that before many years have passed away, Darwin's hopes may be realised,
either with or without the intervention of the "doubly rich millionaire."

Three years after the death of Darwin, the veteran Professor Dana
re-entered the lists and contributed a powerful defence of the theory of
subsidence in the form of a reply to an essay written by the ablest
exponent of the anti-Darwinian views on this subject, Dr. A. Geikie.  While
pointing out that the Darwinian position had been to a great extent
misunderstood by its opponents, he showed that the rival theory presented
even greater difficulties than those which it professed to remove.

During the last five years, the whole question of the origin of coral-reefs
and islands has been re-opened, and a controversy has arisen, into which,
unfortunately, acrimonious elements have been very unnecessarily
introduced.  Those who desire it, will find clear and impartial statements
of the varied and often mutually destructive views put forward by different
authors, in three works which have made their appearance within the last
year,--"The Bermuda Islands," by Professor Angelo Heilprin; "Corals and
Coral-Islands," new edition by Professor J.D. Dana; and the third edition
of Darwin's "Coral-Reefs," with Notes and Appendix by Professor T.G.
Bonney.

Most readers will, I think, rise from the perusal of these works with the
conviction that, while on certain points of detail it is clear that,
through the want of knowledge concerning the action of marine organisms in
the open ocean, Darwin was betrayed into some grave errors, yet the main
foundations of his argument have not been seriously impaired by the new
facts observed in the deep-sea researches, or by the severe criticism to
which his theory has been subjected during the last ten years.  On the
other hand, I think it will appear that much misapprehension has been
exhibited by some of Darwin's critics, as to what his views and arguments
really were; so that the reprint and wide circulation of the book in its
original form is greatly to be desired, and cannot but be attended with
advantage to all those who will have the fairness to acquaint themselves
with Darwin's views at first hand, before attempting to reply to them.

JOHN W. JUDD.