18 AUSTRALASIA. 



few hundred fathoms. The three great Indonesian islands of Sumatra, Java, and 

 Borneo, together with the Mahiy peninsula, all rest on a vast flooded plateau, 

 where the water is scarcely anywhere more than forty fathoms deep. The two 

 great oceanic basins are here separated by a sill some 900 miles broad. Australia 

 and New Guinea may in the same way be regarded as forming upheaved portions 

 of a common submarine bank, which also comprises Tasmania in the south, and in 

 the north several insular groups contiguous to Papuasia. 



But the two regions of the Eastern Archipelago and Australia are separated by 

 a trough over 500 fathoms deep skirting the east side of Timor, while depths of 

 over 2,000 fathoms have been recorded to the south of Ceram. 



In the Pacific properly so called most of the archipelagoes with their dependent 

 chains of reefs also rest on elevated banks, which like that of Central America are 

 nearly all disposed in the direction from north-west to south-east. In the vast 

 semicircle of continental lands sweeping round from the Cape of Good Hope to Cape 

 Horn, the archipelagoes of the Pacific would thus appear to be the scattered frag- 

 ments of a circle resting eastwards on the American seaboard. The disposition of 

 these outer and inner curves ma}' be compared to that of many large breached 

 craters, within which have been developed regular craters of smaller dimensions. 



The deep cavities limited on either side by the elevated banks have received 

 from the English and American explorers names which recall either the vessels 

 employed in the hydrographie surveys of the South Seas, or else the naturalists who 

 have laboured with the greatest zeal in these bathymétrie operations. Thus the 

 circular cavity to the west of Tasmania over 2,000 fathoms deep has been named 

 " Jeffrey's Trough." Here the line recorded at one spot a depth of no less than 

 2,600 fathoms. On the east side of Tasmania in the direction of New Zealand 

 occurs another chasm of larger size and equal depth (Thomson's), which is con- 

 tinued in the north towards Queensland by that of Patterson, thirty or forty 

 fathoms deeper. Those of the Gazelle, running parallel with the general axis 

 of the oceanic islands, that is, in the direction from the north-west to south-east, 

 are somewhat shallower, nowhere exceeding 2,300 fathoms. At their western 

 extremity they are connected with those of Carpenter, which begin at Torres Strait 

 and Papuasia, and terminate between New Caledonia and the New Hebrides. At 

 the deepest point the plummet here recorded 2,630 fathoms, or about three miles, 

 and an equal depth occurs in the Nares pit to the north of New Guinea and New 

 Britain. The cavities are still deeper towards the east, where those of Hildgard 

 and Miller have 3,080 and 3,305 fathoms respectively. 



North of the Carolines the Pacific waters are far less obstructed by insular 

 groups, and, as might have been expected, are proportionately deeper than those of 

 Polynesia properly so called. The cavities named from the CliaUetiger, to which 

 we are indebted for so many important researches in oceanic physiography, offer 

 the enormous depth of 4,575 fathoms between the Carolines and the Marianne 

 group, while farther east in the direction of the Marshall Islands other chasms 

 have disclosed depths of considerably over 3,000 fathoms. Lastly, the wdiole of 

 the North Pacific region between Japan and California presents a vast elliptical 



