96 I<^ ^1 1 ^i president's ADDRESS — SECTION' C. 'i 



members of the group and of raised limestone in the east, but this 

 is lying almost horizontally. Here and at the Kermadecs there is a 

 trench of great depth in close proximity to the island chain on its 

 eastern side. It has in the past been generally thought that this 

 trench should rightly be classed as a " graben " or trough fault, as 

 it was described by Jensen^ and Krummel.^ Suess, however, dis- 

 tinguishes it as a fore-deep. He emphasises the difference of struc- 

 ture of the two sides of the trench. He says : " With one or two 

 exceptions all marine abysses that sink below a depth of 7,000 

 metres are fore-deeps in a tectonic sense, and indicate the sub- 

 sidence of the foreland beneath the folded mountains."^; and on 

 a later page. " The fore-deeps are not synclines in the tectonic 

 sense of the word, for one side belongs to the foreland, the other to 

 the folded mountains." In this particular case it must be remem- 

 bered that all statements about folded mountains are conjectures, 

 for all the exposed sediments — and they are certainly not older than 

 the tertiary — are not folded. Again, apart from the difference in 

 the slope of the two sides of the trench, there is no evidence of a 

 difference of structure. It is well known that in the island of Niue 

 on the foreland side there is a series of raised and terraced lime- 

 stones quite similar to those of the Eastern Tonga Islands, though 

 the distance that separates them is less than 250 miles. Whatever 

 the true structure of the Kermadec and Tonga regions may be — 

 analogous to the East Cape region of New Zealand or not — the 

 linear arrangement of the islands strongly suggests that they mark 

 a result of the same earth forces to which the lineal form of New 

 Zealand is due. 



As this line of shallow soundings is followed north of the Tonga 

 group it is found to trend sharply to the west, when it widens out 

 and on its broad surface is found the Fiji group. For our know- 

 ledge of the structure of these islands we are mainly indebted to 

 Woolnough.* Consisting as this group does mainly of lavas and 

 tuffs, there are but few structural matters of importance. An older 

 series of rocks but little exposed strikes N.N.W. to S.S.E. The 

 Tertiary rocks are almost flat, though found at times at an elevation 

 of 4.000 feet. 



Another sharp curve, first west and then north, in the line of 

 shallow soundings, brings us to the New Hebrides. Here Mawson 

 has described tertiary limestones highly inclined with a v'er^' 

 variable strike, though on the whole N.W. to S.E. He regards the 

 structure as due to pressure and overthrusting from the east and 

 subsequently to a down throw on the eastern side.^ The evidence 

 in favour of this view is, however, somewhat fragmentary. So 

 little is known of the soundings to the north of the New Hebrides 

 and of the structure of the Solomon Islands that it can only be 

 said that the arrangement of the islands supports the view that 



1 Jensen, H. 1. : Proc. Linn. Soc. N.S.W., 1906, p. 141. 



2 krummel, O. : " Handbuch der Oceanographie," 1907, p. 126. 



:? Suess, E. : " The Face of the Earth," vol. IV., 1909, p. 295 and p. 627. 



4 Wooluoiigh, W. G. : .\ contribution to the Geology of Viti Levu, Fiji, Proc. Linn. Soc. N.S.W. 



1907, p. 431. 



5 Mawson, D. : "The Geology of the New Hebrides," Proc. Linn. Soc. X.S.IV'., 1905, p. 400 



