GEOLOGY. 24? 



represented coral structures in their actual original position, 

 and inclined rather to regard it as a stratified accumulation of 

 coral debris^ embedding sometimes larger masses of coral 

 colonial growths. Chamisso followed Forster in supposing 

 that the coral reefs began to take shape on the ocean-floor at 

 considerable depths, and their own continued growth brought 

 them ultimately up to the surface. At the same time, from the 

 distribution of coral islands, Chamisso thought it probable 

 that corals settled upon submarine ridges. Eschholz associ- 

 ated the form of the coral islands with the pre-existing form of 

 submarine mountains, whose summits they crown. He ex- 

 plained the origin of atolls on the assumption that when a reef 

 has arrived at considerable dimensions the corals flourish best 

 on the outer edge under the constant wash of the breakers 

 and surf, and the reef tends therefore to increase more rapidly 

 there ; the lagoon, which is seldom over 30 fathoms deep, in 

 the opinion of Eschholz, arises from the decrease and even 

 cessation of coral growth in the middle of the reef, where the 

 refuse of molluscan shells and coral fragments accumulates 

 and militates against the proper nourishment of the corals. 



Immediately following the results of the Kotzebue Expedi- 

 tion, those of the Freycinet Expedition in the years 1818-20 

 became known. Quoy and Gaimard published their observa- 

 tions on the mode of life of reef-corals in the Annales des 

 Sciences naturelles in 1825. They never found living reef- 

 corals in greater depths than 25-30 feet, and therefore con- 

 cluded that these polyps could only exist in shallow and warm 

 water, and preferentially in protected bays little affected by 

 storms. Judging also from the small thickness of the raised 

 coral limestones at Timor, Ile-de-France, New Guinea, and 

 the Sandwich Isles, they argued that coral reefs could never 

 be very thick. In confirmation of this result they mentioned 

 how frequently coral reefs occur in a direction continuing 

 that of the mountain-chains on land, while the massive reefs 

 are limited to submarine platforms sloping gently from the 

 shore. 



Henrik Steffens in 1822 suggested that coral atolls formed 

 on the summit of submarine volcanoes around the crater of 

 eruption, which was afterwards occupied by the central lagoon 

 of the reef. The same hypothesis was advanced indepen- 

 dently by Quoy and Gaimard, and during the Duperry Expedi- 

 tion of 1828 was more closely investigated and accepted by 



