Interesting Study of Coral Reefs. 117 



atoll was a submerged and lofty mountain, with a 

 summit ten miles across, and sides more precipitous 

 than any peak on land. " Every single atom," he 

 says, " from the least particle to the largest fragment 

 of rock in this great pile, which, however, is small 

 compared with very many other lagoon-islands, bears 

 the stamp of having being subjected to organic 

 arrangement. We feel surprise when travellers tell 

 us of the vast dimensions of the Pyramids and other 

 great ruins, but how utterly insignificant when com- 

 pared to these mountains of stone, accumulated by 

 the agency of various minute and tender animals ! 

 This is a wonder which does not at first strike the 

 eye of the body, but, after reflection, the eye of 

 reason." 



Much time and attention was devoted to the study 

 of coral reefs while here, and later was given to the 

 world the results of the naturalist's investigations on 

 the theory of subsidence, which caused no little con- 

 troversy between Darwin, Semper, and several others. 



Darwin found three classes of reefs : atolls, barrier, 

 and fringing reefs, and by a careful system of dred- 

 ging from the Beagle became convinced that reef coral 

 does not grow in a greater depth than one hundred 

 and eighty feet. From this he assumed that there 

 must have been an original base for all the coral 

 islands at a depth greater than that given. He saw 

 banks and shoals in the ocean miles in length, and in 

 one case fifteen hundred miles long where it would 

 seem impossible for the deposit to have been made 

 by currents or winds. How, then, was the base of 

 the coral island deposited ? An elevation of beds of 



