250 Transactions. 



geological antiquity ; the second includes Tertiary to Recent formations 

 of volcanic and sedimentary origin. Between these two is an enormous 

 hiatus." This admits of three explanations : — 



(1.) The area may have been one of prolonged and continuous sub- 

 sidence since very early geological time, and the land may have 

 been gradually decreasing in size, with an elevation of nearly 

 1,300 ft. since Tertiary time. 

 (2.) The land may have been one of continual elevation, denudation 



keeping pace with uplift, so that no trace is left. 



(3.) A third, that land was in existence in Palgeozoic and Mesozoic 



times, and then followed a subsidence, during which the 



Tertiaries were laid down, and then there was an elevation. 



These three hypotheses are thus stated by Dr. Woolnough. He incUnes 



to the first, whereas Wichmann beheved in the last. Wichmann's theory 



apparently explains the biological facts as demanded by Hutton, Pilsbry, 



Hedley, Von Ihering, and Baur. It is possible that the Tertiary subsidence 



extended all over the south-western Pacific, and the recent elevation of Fiji 



has its counterpart in the recent elevation of the Kermadecs and Tonga. 



If this is so, the Kermadecs were cut off from Fiji in early Tertiary times, 



and rose at a later date, with probable periods of oscillation, either as a 



volcanic cone from a shallow sea or as a cone on a small area of plutonic 



rock which is now covered with a veneer of volcanic fragmentary material 



and lava-flows. 



Further to the westward the presence of Triassic and Jurassic sedimentaries 

 in New Caledonia is proof that shallow- water conditions extended over a 

 large part of the area in Mesozoic times, with the implied presence of a 

 land-mass in the neighbourhood of such a size that thick and extensive 

 sediments could be derived from it. 



The suggestion of a continental origin for the Kermadec Islands appears 

 to be following the present tendency to reduce the number of oceanic islands. 

 It is highly probable that many volcanic islands classified as oceanic will 

 ultimately have to be looked on as built up on the remnants of a conti- 

 nental area. When we consider that the Galapagos Group — thought to be 

 typically oceanic by Wallace and Darwin, although the latter had doubts 

 about it — has been proved lately by Baur and Hemsley to be certainly of 

 continental origin on biological grounds, the case of the Kermadecs, stated 

 so decidedly by Cheeseman and Percy Smith, is perhaps open to revision. 

 If their claims to be classified as continental are worthy of serious considera- 

 tion (which indeed I think is the case), then they, with the volcanic Norfolk 

 Island and Lord Howe Island, would form the northern outlier of the New 

 Zealand continent, just as the Snares, Auckland Islands, Campbell Islands, 

 Bounty Islands, Antipodes Islands, and Macquarie Islands form its southern 

 outliers. 



PETROLOGY OF THE KERMADEC ISLANDS. 



The only previous reports on the rocks of the Kermadec Islands are those 

 of Professor Thomas (Trans. N.Z. Inst., vol. xx, p. 311, 1888) and of the 

 present author (Trans. N.Z. Inst., vol. xxviii, p. 625, 1896). The former 

 reports the occurrence in the group of basalt, augite andesite, pitchstone, 

 obsidian, as well as of a hornblende granite ; and the latter mentions augite 

 andesites and also a tachylyte. With the exception of the granite, all the 

 rocks are volcanic. The present collection no doubt contains some of those 

 previously described, as neither Professor Thomas nor myself has visited 



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