THE GORGONACE^ AS A FACTOR IN THE 

 FORMATION OF CORAL REEFS. 



By L. R. Gary. 



INTRODUCTION. 



An important constituent of the limestone of coral reefs is the cal- 

 cium carbonate secreted in the skeletal structures of Anthozoa and marine 

 calcareous algae. Representatives of the Hydrozoa were important reef- 

 formers in past geological epochs, but in the formation of modern reefs they 

 constitute a minor factor. Representatives of the Anthozoa — the stony and 

 flexible corals — are among animals the only important contributing agents 

 in the formation of the modern reefs. 



The formerly prevailing idea as to the relative importance of animal and 

 vegetable organisms in reef formation underwent extensive change as a 

 result of the borings at the island of Funafuti, in the Ellice Islands, made 

 under the direction of a committee of the Royal Society of London. The 

 examination of the cores from these borings showed that in this particular 

 region calcareous algae of the genus Halimeda had been a very active agent 

 in the accumulation of limestone. At the bottom of the lagoon there was a 

 depth of somewhat more than loo feet where the deposit was made up almost 

 entirely of the remains of this form and the skeletons of Foraminifera. In 

 the body of the reef, and at a greater depth at the bottom of the lagoon, the 

 abundance of material formed by the activity of these algae was very much 

 less than in the former boring, so that, when the entire deposit of limestone 

 is considered, the algae are a much less important factor than is indicated by 

 the character of the surface deposits within the lagoon. Foraminifera and 

 "other organisms" were found to make up a considerable portion of the 

 limestone brought up in the course of both borings. 



Of the animals which (by their power of secreting calcium carbonate 

 from sea-water) have been designated as reef-builders the Madreporaria, 

 among modern forms, have attracted the most attention on account of 

 the character of their skeleton. In all these animals the skeletal growth is 

 apparent from the early development of the colony, and after the death of 

 the polyps the skeleton retains for a long time those structural characteristics 

 which distinguish the different species. Of the Alcyonaria, those types alone 

 which secrete a massive skeleton, i. e., one in which the spicules are fused to 

 a solid mass, have received adequate consideration as contributing to reef 

 formation. Many of the other Alcyonaceae, which when alive form much 

 larger colonies than those last-mentioned, leave no conspicuous remains, 

 as the skeletal spicules are scattered soon after the death of that portion of 

 the colony by which they were secreted. 



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