president's address — SECTION c. 97 



the structural line is continued through the Solomon Islands to the 

 New Ireland and Admiralty Islands. 



The rocks of the islands situated along the line mentioned are 

 sufficiently similar to support the idea of its tectonic continuity. 

 On the western side of the structural axis of the North Island of 

 New Zealand the volcanic rocks are andesites, generally of some- 

 what basic types. Those of the Kermadecs are also almost exclu- 

 sively andesites, but somewhat more basic. The rocks of the Tonga 

 group, so far as known, are also andesites, and this series with 

 basalts are practically the only types in the Fiji Islands, and 

 similar rocks occur again in the New Hebrides and in the Solomon 

 Islands. There is then a remarkable absence of acid and of 

 alkaline rock types in these island groups situated along the line 

 that has been so frequently mentioned. 



At the present time there is a tendency to refer to the andesitic 

 rocks as the " Pacific type " because of their frequent occurrence 

 in the Pacific area. It has, however, been pointed out by Becke^ 

 that the rocks of the Pacific type are connected with foldings by 

 tangential pressure. If this statement be accepted, additional 

 weight is given to the suggestion that the line that passes through 

 the island groups mentioned is one of structural significance. 



The importance of this is reaUsed when it is pointed out that 

 in all the island groups lying to the east of this line only basic and 

 alkaline rocks are known. These types have been shown to exist 

 side by side by Lacroix in Tahiti, by Weber in Samoa, by Wichman 

 in Hawaii, by Velain in Easter Island, by Marshall in Raratonga, 

 Aitutaki, Raiatea and Huaheine. Such rocks are by Becke sup- 

 posed to be associated with inbreaks due to radial contraction, and 

 if this is true it emphasises the structural difference between the 

 islands on the line referred to and the isolated island groups of the 

 Pacific basin. However, if this view is adopted difficulties will be 

 encountered in explaining the occurrence of the alkaline and basic 

 types at Dunedin and Auckland, in New Zealand, though it is true 

 that the abrupt truncation of the folded range at the former place 

 supports the idea of crustal fracture there. Lacroix has lately, in 

 ■discussing the occurrence of alkaline rocks in the Pacific area, 

 suggested in regard to the andesitic or Pacific type that" au moins 

 faut-il parler non d'un facies Pacifique mais d'un facies circum- 

 Pacifique."^ 



From time to time biologists have considered the distribution 

 of plants and animals in the Pacific region, and have arrived at 

 certain conclusions in regard to land extensions at different periods 

 in the past. It is, however, unfortunately true that biologists are 

 not a present in agreement as to the extent and nature of these 

 earlier land connections. Such speculations have been in great 

 part confined to the problems encountered in the far South, and 

 they have varied from Wallace's behef, that no changes need have 

 taken place in the past to account for the present distribution to 

 Forbes's construction of an immense continental area in high 



1 Becke, F. : Min. petr. Mitth., 1903, XXII., p. 209. ~~~ 



2 Lacroix, A.: Comptes Rendus, 151, p. 127, 1910. 



