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 coidd be detected, by 

 chemical or microscojyic means, which suggested the proximity of 

 non-calcareous rocks, even in the lowest j)ortions 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 101^ 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 cora/s, 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 



' The A toll nf Funafuti; Rc'i^ort of the Coral Reef Committee of the Royal Society, 

 London, lOOi. 



