168 "ALBATEOSS" TROPICAL rAClFIC EXPEDITION. 



THE COOK ISLANDS. 



Plates 106, fig. 1; 211; 21J, figs. ;?, 5. 



In the Cook Islands, as in the Fiji group, we find islands composed of 

 elevated coralliferous limestone, like Atiu,^ Mangaia, Mauki ; volcanic islands 

 with comjiaratively limited fringing reefs and barrier reefs, like Rarotonga;" 

 and a series of low reefs, like the Hervey and the Palmerston Islands,^ from 

 which all traces of the central island have disappeared (PI. 212, fig. 3); and 

 atolls, like Aitutaki, with high volcanic peaks. 



Williams,* who visited the Cook Islands, was an excellent ob.server, and 

 his account of various islands is most trustworthy. He recognized in a gen- 

 eral way tlie characteristic geological features which distinguish the islands 

 of the same or of different groups, and he classified the Pacific islands, first, 

 into high volcanic islands, secondly, into elevated limestone islands, and 

 finally, into low coral islands. 



In Atiu and Mauki are extensive caverns, one of which is described in 

 detail by Williams. At Mauki extensive beds of apatite are also said to 

 exist. Williams speaks of Atiu as made up of elevated coral rock, a solid 

 compact mass of limestone. Gill also speaks of Atiu as made up of uplifted 

 coral perforated in ever}' direction by caverns. 



Williams describes at Mangaia a broad ridge (terrace ?), said by him to 

 be 300 feet, at a height of 100 feet. Gill also describes it, and figures 

 the terraces of Mangaia ; he speaks of the occurrence of dark volcanic rock 

 and red clay in the interior of Mangaia. 



Rurutu is said by Williams to be 150 feet in height, while the " Sailing 

 Directions " say the mountains attain a height of 1300 feet. Williams 

 noticed the similarity of the elevated limestone to the streaked basaltic 

 appearance of volcanic rock. Williams also noticed that Savage Island (Nine) 

 was composed of elevated coral reef, and he describes the cuts and caverns 

 found along the shores and inlets. 



1 A. Chart 12C4. ^ Ibid. ^ Ibid. 1176. 



■" Missionary Enterprises, pp. 18, 23, 28, 30, 292. 



