ALEXANDER AGASSIZ MAYER. 469 



The Hawaiian, Paumotos, Society, Cook, Meue, Tonga, Fiji, La- 

 drone, and Caroline Islands all show elevated coral or limestone reefs, 

 but there are no visible indications of elevation in the Marshall or 

 Gilbert Islands where the underlying rock is not lifted above the sea. 

 Makatea in the Paumotos may have been an atoll which was elevated 

 about 230 feet above the sea and with a lagoon basin in the center 

 sunken about 70 feet below the encircling ridge. It is possible, how- 

 ever, that this central concavity may have been formed by solution 

 after the island was raised above the sea, and that the island was not 

 originally an atoll. 



The lagoons of the Pacific atolls were found to be usually from 13 

 to 20 fathoms deep, and to be quite thickly studded with submerged 

 rocks consisting of Tertiary limestone incrusted with modern corals. 



The atoll contours are due to a coordination of complex conditions, 

 erosion, currents, silt, etc., which determine the place and rates of 

 growth of the corals; and not to subsidence, as was postulated by 

 Darwin. 



The modern coral reefs are, according to Agassiz, distinct from 

 the Tertiary limestones, and form a mere crust upon a base of lava or 

 of old limestone. 



A notable act of the expedition was the bringing up of the deepest 

 trawl haul ever made, this being from a depth of 4,173 fathoms, 75 

 miles east of Tonga Tabu. Siliceous sponges were found here under 

 an ocean almost as deep as the crests of the Himalayas are high. 



In Bora Bora, of the Society Group, he found a broken ring of 

 sandy coral islets covered with coco palms, and encircling the shal- 

 low waters of the lagoon, out of the center of which there arises the 

 towering mass of the basaltic cliffs of the island. The sight of this 

 old volcano, now sleeping and encircled by its palm-crowned atoll 

 ring, so impressed Alexander Agassiz that he employed Mr. G. W. 

 Curtis to make a survey, and to construct a detailed model of the 

 island for the museum at Harvard. 



As one goes westward over the tropical Pacific the coral heads 

 upon the reefs become larger and larger, those of the Paumotos 

 being small and stunted, while those of the Great Barrier Keef of 

 Australia are the largest in the world. 



Alexander Agassiz had now seen nearly all of the coral islands ol 

 the Pacific, and he at once turned his attention to the Indian Ocean, 

 cruising among the atolls of the Maldive Islands from December, 

 1901, to January, 1902. For this purpose he chartered the steamer 

 Amra from the British India Steam Navigation Co., William Pigott, 

 R. N. R., in command. He steamed more than 1,600 miles among 

 the islands, making more than 80 soundings. Mr. J. Stanley Gardi- 

 ner, M. A., had only recently explored the Maldives, and his account 

 of their mode of formation was published before that of Agassiz. 



