370 Darwin and Geology 
necessary by Darwin, was as follows :—The whole of the cores are 
found to be built up of those organisms which are seen forming 
coral-reefs near the surface of the ocean—many of them evidently 
in situ; and not the slightest indication could be detected, by 
chemical or microscopic means, which suggested the proximity of 
non-calcareous rocks, even in the lowest portions brought up. 
But this was not all. Professor David succeeded in obtaining the 
aid of a very skilful engineer from Australia, while the Admiralty 
allowed Commander F. C. D. Sturdee to take a surveying ship into the 
lagoon for further investigations. By very ingenious methods, and 
with great perseverance, two borings were put down in the midst of 
the lagoon to the depth of nearly 200 feet. The bottom of the 
lagoon, at the depth of 1014 feet from sea-level, was found to be 
covered with remains of the calcareous, green sea-weed Halimeda, 
mingled with many foraminifera ; but at a depth of 163 feet from the 
surface of the lagoon the boring tools encountered great masses of 
coral, which were proved from the fragments brought up to belong to 
species that live within at most 120 feet from the surface of the 
ocean, as admitted by all zoologists’. 
Darwin’s theory, as is well known, is based on the fact that the 
temperature of the ocean at any considerable depth does not permit 
of the existence and luxuriant growth of the organisms that form 
the reefs. He himself estimated this limit of depth to be from 120 to 
130 feet; Dana, as an extreme, 150 feet; while the recent very pro- 
longed and successful investigations of Professor Alexander Agassiz 
in the Pacific and Indian Oceans lead him also to assign a limiting 
depth of 150 feet; the effective, reef-forming corals, however, flourish- 
ing at a much smaller depth. Mr Stanley Gardiner gives for the 
most important reef-forming corals depths between 30 and 90 feet, 
while a few are found as low as 120 feet or even 180 feet. 
It will thus be seen that the verdict of Funafuti is clearly and 
unmistakeably in favour of Darwin’s theory. It is true that some 
zoologists find a difficulty in realising a slow sinking of parts of the 
ocean floor, and have suggested new and alternative explanations: 
but geologists generally, accepting the proofs of slow upheaval in 
some areas—as shown by the admirable researches of Alexander~ 
Agassiz—consider that it is absolutely necessary to admit that this 
elevation is balanced by subsidence in other areas. If atolls and 
barrier-reefs did not exist we should indeed be at a great loss to 
frame a theory to account for their absence. 
After finishing his book on Coral-reefs, Darwin made his summer 
excursion to North Wales, and prepared his important memoir on 
1 The Atoll of Funafuti; Report of the Coral Reef Committee of the Royal Society, 
London, 1904. 
