278 Transactions. 



gewonnenen Ergebnisse, so muss jede unbefangene Diskussion die Tatsache 

 anerkennen : dass die marinen Ablagerungen der oberen Kreide von 

 Patagonien eine starke, successive Abnahme von mesozoischen Charakter- 

 formen aufweisen, dass aber andererseits diese letzteren sick zum Teil 

 erhalten, dass mithin die Elemente der Kreidefauna teils unverandert, teils 

 modifiziert in die patagonische Formation iibertreten und dass keine Dis- 

 cordanz zwischen der Kreide und den Ablagerungen der patagonischen 

 Formation besteht."* 



So far as New Zealand is concerned, then, it appears to be probable 

 that at the close of Cretaceous times a great movement of epeirogenic 

 depression took place. The land area was reduced to the dimensions of a 

 few small islands. Over much of the present land area deep-sea oozes 

 were deposited for a great lapse of time. Marginal deposits were restricted 

 and small. When elevation again commenced the Upper Cretaceous fauna 

 had been replaced by one of Tertiary characteristics. 



Art. XXVIII. -- Notes on the Geology of the Tubuai Islands and of 



Pitcairn. 



By P. Marshall, M.A., D.Sc. 



[Read before the Wanganui Philosophical Society, 19th December, 1917 ; received by 

 Editors, 31st December, 1917 ; issued separately, 24th June, 1918.] 



The scattered islands which constitute the Tubuai Group are situated 

 near 23° south latitude and 150° west longitude. Little geological infor- 

 mation has been published about them except in regard to their general 

 configuration and the nature of the coral reefs by which they are encircled. 



A visit has lately been made to the group by Professor J. Macmillan 

 Brown in connection with his anthropological studies, and he has been good 

 enough to give me chips from implements that he obtained from Tubuai 

 and Rapa. In addition, the Chief Magistrate of Pitcairn sent me several 

 specimens from that island. I have previously published a note on rock- 

 specimens from Rurutu Island, another member of the Tubuai Group. f 



Stone Axe, Tubuai Island. — A dense black rock in hand-specimens. 

 In section the structure is dominated by an abundance of small laths of 

 feldspar with the extinction angle of labradorite. There are a few large 

 crystals of olivine much serpentinized. There is also a little olivine in the 

 oroundmass. Augite is very plentiful in the groundmass in small colourless 

 trains. Magnetite very abundant. The rock must be classed as a dense, 

 rather acid basalt. 



Stone Axe, Rapa Island. — In hand-specimens a dark fine-grained rock 

 without any crystals that can be distinguished macroscopically. In section 

 fine laths of feldspar are very abundant. They appear to be an acid 

 labradorite or andesine. Augite is very plentiful, but the grains seldom 

 have any crystalline outline, and they are quite colourless. A little olivine 

 is present in very irregular-shaped grains. Magnetite is very plentiful in 

 crystals up to 0-2 cm. in diameter. A little apatite can be distinguished. 

 This rock is also an acid feldspathic basalt, and, like the specimen from 

 Tubuai, it has an unusual quantity of magnetite 



* Von Iheeing, Revista do Museu Paulisia, vol. I, Fasc. 3, p. 130 Sao Paulo, 1914. 

 f Trans. N.Z. Inst., vol. 46, p. 283, 1914. 



