162 Transactions. — Geology. 



All the sedimentary rocks up to the Hokanui system 

 (Lower Jurassic) inclusive partake of the flexures in the 

 mountains ; while those of the Waipara system (Upper Cre- 

 taceous) are also involved to some extent in Otago and Nelson. 

 But the rocks of the Oamaru (Oligocene) and younger series 

 either retain their original plane of deposition or are occasion- 

 ally distorted locally. 



In the North Island the structural axis appears to be 

 continued through the centre of the Island from Wanganui to 

 the Bay of Plenty, and the chief mountain-range lies to the 

 west of it, as in the South Island. This main range is formed 

 by rocks belonging to the Maitai (Permo-carboniferous) and 

 Hokanui systems, smothered on each side by Tertiary beds 

 through which isolated ridges and peaks of the older Maitais 

 and Hokanuis rise at intervals throughout the Auckland 

 Province. 



To the south-east of the main range in both Islands vol- 

 canic rocks occupy but a small area ; but on the north-western 

 side, from the centre of the North Island to iVuckland, they 

 cover more than half the country, and appear again in great 

 force further north, between Hokianga and the Bay of 

 Islands. 



Wanaka System. 



The oldest rocks in New Zealand are the crystalline 

 schists of Central Otago, which have been called the 

 "Wanaka system."* They are largely developed in the in- 

 terior of Otago from the Taieri to the great lakes, and from 

 thence they pass north, m a narrow band, at the western 

 foot of the New Zealand Alps, as far as the Spencer Moun- 

 tains, in the Nelson Provincial District. In Otago they 

 appear to have the enormous thickness of not less than 

 100,000 ft., or about nineteen miles. The lower part of the 

 system is formed principally of mica-schists, varying from 

 coarsely foliated rocks with thick lenticular plates of quartz 

 to finely foliated, with nearly parallel folia. These pass up- 

 wards into fine-grained mica-schists, silky phyllites, clay- 

 slates, and quartzites. 



Similar schistose rocks appear in Queen Charlotte Sound 

 and the Pelorus ; also in Collingwood County, at the mouths 

 of the Aorere and Parapara Rivers. But each of these dis- 

 tricts is separated from the main body of schists in Otago and 

 Westland by younger rocks, which cross the Upper Buller 

 from the Spencer Mountains to the Wangapeka Eiver, and 

 which hide the older schists. One of these detached portions 

 — that near the mouth of the Aorere Eiver — is overlain, appa- 



* " Report on the Geology and Goldfields of Otago," p. 29 ; Hutton 

 and Ulrich, Dunedin, 1875. 



