16 Proceedings of the Royal Physical Society. 



of the corals on the external faces of the reef, in presence of 

 abundant food; by their death, disintegration, and removal 

 by the mechanical and chemical action of the sea in the inner 

 parts ; and by the influence of subaerial agencies and breaker- 

 action, in lowering the level of the upraised areas of coral-rock. 

 The most detailed investigation of coral-reefs which has yet 

 appeared, has recently been published by Professor A. Agassiz.^ 

 This able naturalist is engaged in prosecuting a series of 

 researches into the biological phenomena of the seas on the 

 eastern side of the United States, under the auspices of tlie 

 United States Coast Survey, and in the course of these 

 explorations, has had occasion to devote himself to the 

 detailed study of the coral-reefs of the Florida seas. For 

 purposes of comparison, he has likcAvise visited the reefs 

 among the West Indian Islands, as well as those on the coast 

 of Central America. His observations are thus the most 

 exhaustive and methodical which have yet been published, 

 and the deliberate conclusions to which he has come deserve 

 tlie most attentive consideration. He traces the history of a 

 coral-reef from its latest stages as dry land to its earliest 

 lieginnings, and even beyond these, to the gradual evolution 

 of the conditions requisite for the first starting of the reef. 

 His familiarity with the nature of the bottom all over the 

 area in question, and with the life so abundant in the troj)ical 

 waters, gives him a peculiar advantage in this inquiry. The 

 upheaval of recent coral-formations to considerable lieights 

 above the sea, in various parts of the region, enabled him to 

 examine the inner structure and foundations of the reefs, and 

 to obtain therefrom altogether new data for the solution 

 of the problem. Following him in his induction, we are led 

 back to a comparatively recent geological period, when the 

 site of the peninsula of Florida was gradually upraised into 

 a long swell or ridge, having its axis in a general north and 

 south direction, sinking gently towards the south, but pro- 

 longed under the sea as a submarine ridge. The date of this 

 elevation is approximately fixed by the fact that the Vicks- 

 burg limestone was upraised by it, and this limestone is 

 assigned to the upper Eocene series. As a consequence of 



1 On the Tortugas and Florida Reefs (Trans, Amer. Acad., xi., 1883). 



