Marshall. — Geology of North Island. 83 



sediments. As this folding probably took place immediately 

 after their deposition, it appears that the norite can hardly 

 be of Post-Mesozoic age. 



The volcanic rocks extending from Mount Egmont, Ruapehu, 

 and the Bay of Plenty northward have not received much atten- 

 tion, so far as general statements are concerned, since Hoch- 

 stetter's time. Apparently he made extensive collections, but 

 only a few of his specimens appear to have been submitted to 

 microscopical or chemical examination. A few of them, how- 

 ever, were described by Zirkel.* All of them are classified as 

 rhyolites, though with very different structures in the different 

 specimens. Of those examined, the majority were collected 

 near Taupo and near Rotorua, though there were examples of 

 obsidian from Tuhua as well. Mica was identified in many 

 examples, but no rhombic pyroxene. 



As a result of his observations, Hochstetterf classed the 

 whole of the volcanic rocks of New Zealand in two divisions, 

 called an older and a younger series. The different occurrences 

 in the region under discussion were classed as follows : — 



I. Older volcanic rocks. Tertiary and older Quaternary (Pluto- 



volcanic). 

 (a.) Northward of Auckland Harbour, on the west. Ande- 



site and dolerite breccias, with dykes of basalt. 

 (b.) South of Manukau, and thence to Aotea Harbour. 



Basalt conglomerates and basalts without distinct 



cones. 

 (c.) Volcanic table-land between upper and middle Wai- 



kato. Pumice and trachyte tuffs, with old extinct 



craters of trachytic, andesitic, and doleritic rocks. 



II. Younger volcanic formation. Acid and basic products. 



Cones with distinct or stuffed-up craters, 

 (a.) Taupo zone. Rhyolitic and trachytic lavas. Obsi- 

 dian and pumice important. Includes the large 

 volcanoes around Taupo. 

 (b.) Mount Egmont. This may belong to the older period. 

 (c.) Auckland zone. Sixty-three eruption-points, with dis- 

 tinct craters and lava-flows. 

 (d.) Bay of Islands. Between Hokianga and Bay of 

 Islands. Similar to Auckland zone. 

 Since Hochstetter's time important work has been done by 

 Professor Thomas. The results of his first paperf may be 

 thus summarised : Augite-andesites were found at Mount Edge- 

 cumbe ; Ngauruhoe ; Ruapehu, west side ; Wanganui River, 



* " Reise der ' Novara ' : Geologie," vol. i, p. 109. 

 t " Reise der ' Novara ' : Geologie," vol. i, p. 200. 

 J Thomas, Trans. N.Z. Inst., vol. xx, p. 306 et seq. 



