The coral reefs of the Hawaiian Islands

Agassiz, Alexander

Agassiz gives a thorough review of previous ideas of coral reef formation in the Pacific, beginning with observations by Chamisso on Kotzubue's voyage of 1821 (Kotzubue, 1821, v. 3, p. 331). Few of the early references, including Chamisso, mention Hawaii but provide background information for evaluating the formation of reefs in the Hawaiian islands. Agassiz' purpose in providing background is to demonstrate alternatives to Darwin's (1842) theory of subsidence. Beginning on p. 144, Agassiz describes his own observations on the Hawaiian Islands while summarizing the work of others. He notes the different kinds of coral rock, i.e., compact reef rock, 'pudding-stone' (volcanic beach pebbles cemented by calcium carbonate), and coral sands. He gives data for wells that have penetrated coral and describes charred wood recovered from one well as evidence of material washed down from shore and not necessarily as evidence for subsidence. He then describes alternation of coral and lava in the drill holes as indicating ' . . . the gradual extension seaward of the shore line as fast as lava detritus was washed down or flowed over from successive eruptions, while the growth of the layers of coral indicates the period of rest during which the coral beds were deposited, each in its own turn being overwhelmed by a layer of lava or laval detritus, until we reach the existing condition of things.' He concludes that, from the evidence of coral deposition, 'there appears to be no evidence that there has been any considerable elevation of the Hawaiian islands, twenty to twenty-five feet being probably the extreme; while the presence of cinder cones with their base close to the present sea level would indicate also that there had been no special subsidence.' He continues 'there have yet been no sunken reefs discovered in any of the channels between the islands . . .'. Agassiz does, however, recognize subsidence of the coastline at Kalapana and Kaimu on the island of Hawaii, illustrated by a photograph entitled 'the sunken coral sand beach at Kaimu.¦ Agassiz describes coral formations on islands other than Oahu, including a patch of elevated coral on the edge of the sunken plain of Kalapana. On Maui, he interprets the occurrence of coral sands 500-800 above sea level on West Maui volcano as follows: 'The existence of coral sandstone on the east slope of West Maui at a considerable height, over extensive tracts, does not indicate any elevation, but is due merely to the aeolian deposits which have found their way to certain favorably situated places under the action of the prevailing trade winds. Nowhere in the district I have examined on Maui have I succeeded in finding any trace of corals beyond the height to which fragments might be carried by the action of the waves or wind and tides of unusually severe storms. The bedding of the sandstones at considerable heights was evidently entirely due, as has been shown by Dana, to the successive deposits of sand cemented together by interrupted rain fall, forming the delicate crusts which separate the various thin layers of coral sandstone which have accumulated at certain points.' He similarly interprets the elevated deposits of 200 feet on one side of Diamond Head and near Wailuku, Maui

The coral reefs of the Hawaiian Islands

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