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CARNEGIE INSTITUTION OF WASHINGTON. 



confirms the Director's observations that there are no limestones of 

 any sort upon the elevated shore-bench, which is found all around 

 Tutuila, except ofT the recent lava-flow between Tafuna and Sail Rock. 

 This shows that at one period the island was not surrounded by coral 

 reefs and is in conformity with the conclusion that the present living 

 reefs of Tutuila are not superimposed upon any ancient reefs, but have 

 simply grown outward upon the wave-washed shore-slopes and spur 

 ends since post-glacial times, the remarkably rapid growth-rate of 

 Pacific corals necessitating this conclusion. 



Alfred G. Mayor extended his observations upon growth-rate of 

 Samoan corals by planting weighed, measured, and photographed 

 corals at depths ranging from shallow water to 8.5 fathoms. Experi- 

 ments upon the growth-rate of Lithothamnion and upon the loss in 

 weight of dead and corroding coral-heads were also instituted. Using 

 a diving-hood, he made a somewhat detailed study of the submarine 

 seaward wall of the reef of Tutuila. In regions subjected to heavy 

 breakers the Acropora and Pocillopora constitute 97 per cent of the 

 coral-heads at depths of 1 to 4 fathoms, and these genera have the 

 most rapid growth-rate of all Pacific corals. In silted regions the 

 submerged outer wall of the reef is composed chiefly of branched Pontes, 

 a genus which is extremely rare on the submarine slopes fronting the 

 open ocean. In quiet regions of pure water free from silt a great vari- 

 ety of corals constitute the fauna of the submerged walls of the reef. 



Below 4 or 5 fathoms the coral-heads are generally smaller and not so 

 numerous as they are at lesser depths, and at 8.5 fathoms fronting the 



