254 Mr. John Mitrraij [March 16, 



Soutli America, a circumstance evidently connected with the low 

 temperature, wide range, and, more directly, with the food supply, 

 consequent on these conditions. It appears to be a confirmation of 

 this view that, on the eastern shores of Africa, about Cape Gardafui, 

 from off which the south-west monsoon blows for several months in 

 the year, cold water is also drawn to the surface, and there, likewise, 

 are no coral reefs, though they flourish to the north and south of this 

 region. 



Coral reefs flourish in mid-ocean and along the eastern shores of 

 the continents, or wherever the coasts are bathed by the warmest 

 and purest currents of water coming directly from the open sea. 

 If we except Bermuda and one or two other outlying reefi?, where the 

 temperature may occasionally fall to 66° Fahr. or 64° Fahr., it may 

 be said that reefs are never found where the surface temperature of 

 the water, at any time of the year, sinks below 70° Fahr., and where 

 the annual range is greater than 12° Fahr. In typical coral reef 

 regions, however, the temperature is higher and the range much 

 less. 



The food supply of the coral reef is derived from pelagic oceanic 

 organisms, which exist in the greatest variety and abundance in the 

 surface and sub-surface waters of the ocean. These consist of 

 myriads of algrc, rhizopods, infusorians, mcdusjT), annelids, molluscs, 

 crustaceans, ascidians, and fishes. A very large numbgr of these 

 creatures, within the tropics, secrete carbonate of lime from the 

 ocean to form their shells and skeletons, which, falling to the bottom 

 after death, form the vast oceanic deposits known as Pteropod and 

 Globigerina oozes. In falling to the bottom, they carry down some 

 of the organic matter that composed their living bodies, and thus arc 

 the animals which live on the floor of the ocean chiefly supplied with 

 food. Here it may be remarked that the abundance of life at depths 

 of even over two miles is very great. Our small dredges sometimes 

 bring up over sixty species and hundreds of specimens in one haul — 

 of invertebrates and fishes, exclusive of the protozoa. These pelagic 

 organisms oscillate from the surface down to about 80 or 100 fathoms, 

 probably that stratum of the ocean affected by sunlight, and they 

 ax^parently descend further in regions where the stratum of warm 

 water has a greater depth. Many of the forms rise to the surface in 

 the evening and during calms, and sink again in sunlight and during 

 stormy weather. It is in the evening and when it is calm that this 

 swarming life is most vividly forced on the attention by gorgeous 

 phosphorescent displays. The lime-secreting organisms, like Cocco- 

 spheres and Ehabdospheres, Foraminifera, Pteropods, and other 

 Molluscs, are much more abundant, both in species and individuals, 

 in the warmest and saltest waters than elsewhere. I have estimated, 

 from tow-net experiments, that at least 16 tons of carbonate of lime, 

 in the form of these shells, exist in a mass of the ocean, in coral 

 reef regions, one mile square by 100 fathoms in depth. If we take 

 this estimate, which I consider much below the reality, and suppose 



