DEPTHS OF LAGOONS AND PLATFORMS 559 



readied 45 fathoms and no. bottom. A dei)th of 105 meters, or 57 fath- 

 oms, is given in the latest German chart of the great lagoon of Trnk, in 

 the western Carolines. A depth of 60 fathoms occurs well inward from 

 the margin of a bank or platform that surrounds the often-cited island of 

 Fauro, figure 11, in the Solomon group, and a depth of 58 fathoms is 

 recorded in a space inclosed between Fauro and several smaller islands; 

 this strongly suggests that recent subsidence of Fauro has taken place. 

 It may be inferred also that the subsidence was rapid because there is no 

 barrier reef around most of the bank margin and only a narrow uncon- 

 formable fringing reef on Fauro itself. 



The "sunken barriers^' of New Guinea are strongly indicative of un- 

 equal subsidence. One such example occurs off the eastern part of the 

 south coast, where the normal barrier reef, vv^hich incloses a lagoon from 

 7 to 20 miles in width and from 40 to 50 fathoms in depth, is replaced 

 for a long stretch by a submerged reef at a depth of 5 or 10 fathoms. 

 Again, east of New Guinea, a large barrier reef incloses a lagoon that 

 measures 115 miles in length by 27 miles in width, and from 30 to 45 

 fathoms in depth, within which rise tlie large island of Tagula, 40 by 8 

 miles in diameter and 2,645 feet in height, and many smaller islands; 

 the southwestern part of this barrier is submerged to depths of 6 or 8 

 fathoms for a distance of 15 miles. Only 13 miles to the north of this 

 fine barrier system, and separated from it by sea depths of 700 or 900 

 fathoms, stands Misima, 22 miles long and 3,400 feet high, with no sea- 

 level reefs around it, though Jack and Etheridge briefly mention an 

 island of that name in their account of New Guinea as bearhig elevated 

 reefs. Differential movements seem essential here. The same is true of 

 the Solomon group, where, in addition to the submerged platform of 

 Fauro, above mentioned, submerged and emerged reefs occur in abun- 

 dance. 



It may of course be urged that New Guinea and the Solomon Islands, 

 being far removed from the atoll region of the central Pacific, do not 

 afford evidence of the conditions under which atolls have been formed: 

 but in reply it may be stated, first, that barrier reefs and their lagoons, 

 which are largely developed around New Guinea and the Solomons, re- 

 semble atoll reefs and their lagoons too closely to ascribe them to unlike 

 processes of origin; and second, tliat atolls, thougli rare in the western as 

 compared with the central Pacific, nevertheless occur there in significant 

 numbers. Thus 170 miles north of the Solomon Islands the exceptionally 

 large atoll of Ongtong-Java has a diameter of about 70 miles, and Tasman 

 atoll, about 10 miles; and 120 miles to the south, Rennell Island, an up- 

 lifted atoll, has a length of 50 miles. Woodford has given accounts (1909, 



