452 Transactions. — Geology. 



Art. LIX. — Notes on the Geology of the Bluff District. 



By W. S. Hamilton. 



[Read before the Southland Institute, 2\st January, 1886.] 



Now that the Bkiff is becoming a sea-side resort to the inhabi- 

 tants of the district, as well as a place of call, and often of a 

 little detention, to strangers passing to and from the Australian 

 Colonies, it may be interesting to some to know a little of its 

 geology. The first thing that will attract the attention of the 

 visitor who has an eye to the rocks will be the I'agged slaty 

 strata standing on edge, and striking N.W. and S.E., exposed 

 between low and high water, and in some places considerably 

 above, and flanking the hill from the pilot station to the jetty. 

 These, according to Dr. Hector, belong to the Devonian period, 

 and to the great series of palaeozoic rocks that form the back- 

 bone of New Zealand, or, in other words, the axis of the great 

 mountain system extending from Auckland to Stewart Island. 

 On closer examination, these argillaceous slates are seen to be, 

 at least near the jetty, interstratified with bands of syenite, or 

 granite, from a few inches to several feet thick, becoming more 

 granitoid towards the base of the hill, which is a solid mass of 

 syenite. This would almost lead one to suppose that the hill 

 itself had once been a mass of slate formations of similar age, 

 and that it has been granitized by metamorphic action, and 

 that, at the present junction with the slates, the bands of 

 interstratified granite are only the more silicious layers which 

 have become granitized ; while the more argillaceous layers 

 have withstood the dying-out metamorphic action. 



This appearance Captain Hutton says he is " positive is 

 fallacious," and holds the opinion that the whole range from 

 the New Eiver Heads to Kuapuke is an immense dyke of intru- 

 sive syenite. I am not aware that Dr. Hector gives an opinion 

 on this point ; but from the fact that in his Geological Map it is 

 coloured as metamorphic, instead of true granite or volcanic, it 

 would appear that he inclines to this view. It may also be 

 observed here that Mount Anglem, and the northern half of 

 Stewart Island, is also coloured in his map as metamorphic, 

 while the southern half of the island is coloured as true granite, 

 the same as the West Coast. There can be very little doubt, 

 however, that Captain Hutton's view is the correct one, and 

 that both Mount Anglem and the Bluff Range are of volcanic, or 

 at least of eruptive, origin. Conclusive proofs of this are seen 

 in following round the beach from the Bluff to the Greenhills 

 railway-station. For a mile or two the interstratified bands of 

 syenite or diorite are parallel with the slate and the base of the 



