president's address — SECTION c. 75 



The Post-tHokonm and Earlier Epochs of Orogeny and Plutonic 



IntrU'Sion. 



In the course of the Palaeozoic and Mesozoic periods, the New 

 Zealand region may have suffered several epochs of earth-folding, 

 which we are not yet able fully to disentangle, for folding in 

 diverse directions appear to have been superposed upon one 

 another. The various directions of folding have been stated by 

 Suess (1904), Park (1910), and Marshall (1912). The following 

 summary embodies the newer observations, and offers an inter- 

 pretation of the facts rather different from those which have been 

 given. It must, however, be recognised that this is merely a 

 suggestion ; the writer is not in a position to state an opinion on 

 the subject. In the extreme south-west, the strike of the schistose 

 rocks and Ordovician slates is to the ncrth-west, running from 

 Stewart Island to the Bluff and Preservatioii Inlet. It swings 

 round to the north-north-west or north in Dusky Sound, while 

 further north and on the eastern side of the gneissic mass, namely, 



jNIa 



Fig. 4. Section from West (left hand) to East through Aorere Distiict in the North-west 

 of the South Island. (After Bell 1907.) 



1. Ordovician' argillites, greywackes, and quartzite. 2. Ordovician? crystal- 

 line schist and quaitzite. 3. Ordovicifln ? limestone. 4. Acid igneous 

 rotks. 5. Basic igneous rocks. 6. The Haupirl series. 



on the shores of Lake Te Anau, the strike is to the north-east. 

 The information available to the writer suggests either that the 

 gneissic rocks have a dominantly north-easterly strike, and are 

 unconformable with the north-westerly striking schists, (an inter- 

 pretation now favoured by Park*), or that there is an arcuate 

 folding roughly parallel with that further to the north in Western 

 Otago, a hypothesis which is here advanced. Along the west 

 coast northwards from the Sounds, the strike of the Aorere or 

 gneissic rocks is generally to the west of north, though varying 

 from north-west to north-north-east, and the folds are often over- 

 turned towards the west. (Fig. 4.) Bell (1905) has noted this 

 near Mt. Cook, Morgan (1908, 1915), Webb (1910), and Bell 

 (1906), in North Wootland, and the west of the Nelson 

 Province. Hence the strike of these Aorere rocks and .gneisses, 

 though varying, is generally oblique to the direction of the 

 West Coast, and of the Southern Alps. The distinction between 

 the strike of the Southern Alps and that of the north-westerly 



• Private communication. 



