434 PROCEEDINGS OF SECTION E. 



All examination of this map reveals several important features to 

 which reference must l^e made. 



The Tliomson trough occupies the main part of the area between 

 the A^ew Zealand plateau and Australia. It narrows to the north- 

 ward, giving- way te the ridge which extends north-westward from 

 the New Zealand plateau. The Thomson trough terminates near the 

 tropic of Capricorn, where depths of less than 1,000 fathoms are 

 almost continuous from Australia to New Caledonia, and from the 

 middle of this Caledonian rise the ridge, pre^aously mentioned as 

 forming the eastern limit of the Thomson trough, extends south-south- 

 west, and bending to south-west reaches the New Zealand plateau. On 

 the extreme west of the ridge is Lord Howe Island, and in its central 

 part a well-marked shoal is found. 



Close to New Caledonia on the south-west there is a small trench, 

 and water more than 1,500 fathoms deep extends some distance south, 

 separating the Howe ridge from the Norfolk ridge, which is parallel 

 to it, and has the Britannia shoal in its centre. A narrow curved ridge 

 unites Fiji and the New Hebrides. The Gazelle basin, uniformly 

 2,000-2,500 fathoms, separates the Norfolk ridge from the Fiji ridge, 

 which runs 500 miles south from the eastern extremity of the Fiji 

 Archipelago. A narrow and shallow trench separates the Fiji ridge 

 from the remarkable Kermaclec and Tonga ridge, which commences 

 near Wallis Island, 150 miles south of the western end of Savaii, and 

 thence continues to the south of the Kermadecs, and is separated from 

 the East Cape of New Zealand by water less than 1,500 fathoms deep. 

 This ridge is commonly i-epresented as composed of two distinct 

 portions, but I can find no records of soundings on the direct line 

 between the two undoubted shallow areas, and the soundings on each 

 side of the ridge are not deeper than those on each side of the Ker- 

 madecs and Tonga areas. I have, therefore, represented the ridge as 

 continuous at a depth less than 1,000 fathoms. A liighly irregular 

 boundaiy separates the Gazelle l)asin from the New Zealand plateau. 

 On the eastern side of the Tonga-Kermadec ridge occurs the most 

 remarkable feature of the south-west Pacific — the profound trench 

 which includes the Tonga deep and the Kermadec deep. In a portion 

 of each of these deeps soundings of over 5,000 fathoms have been 

 made; the deepest is in the Kermadec area, and measures 5,155 

 fathoms. These deeps are usually represented as separated by water 

 of 2,000 fathoms, but there is little more reason for separating them 

 than for separating the Tonga and Kermadec areas of the ridge, 

 though, in this case, the connecting portion of the trench must be 

 extremely nan-ow. Eastward of the Kermadec-Tonga trench the floor 

 of tlie Pacific rises slowly to what appears to be a uniform depth of 

 2,500-"5,000 fathoms over nearly the whole of its western portion. 

 This deptli is slightly exceeded soutli-east of the Chathams. Some of 

 the soundings east of the Cook Islands are rather less, but there is no 

 indication of any submarine ridge joining these islands, which appear 

 for the most part to be huge volcanic mountains, sometimes with a 

 veneer of coral, and reaching to a height of 15,000 ft. to 22,000 ft., in 

 the case of Tahiti, above a nearly level ocean floor. The eastward 

 extension of the New Zealand plateau is, in the present state of our 

 knowledge, badly defined. The southward termination of the Tonga- 



