376 PROCEEDINGS OF SECTION C. 



evaporated solution yields crystals of sodium chloride. This indication 

 of the presence of a felspathoid mineral is supported by staining tests. 

 The mineral is probably nepheline, but it is present in very small 

 quantity. Its presence justifies the classification of the rock as a 

 basanite. The basanite is extremely rich in olivine. Magnesia has a 

 percentage of 10 in the bulk analysis. 



In the crater that is now the Domain cricket ground, in Auckland, 

 there are blocks of a coarse-grained rock that have evidently been 

 expelled during an eruption. Microscopical examination shows that 

 it is a basanite with doleritic structure. The nepheline is abundant ; 

 olivine in elongated crystals. The augite is ophitic, enclosing large 

 crystals of andesine. In places it is intergrown with nepheline, pro- 

 ducing a micrographic structure. Menaccanite is well developed. 

 Except for the presence of felspar, the rock closely resembles the 

 nephelinite of the Lobauer Berg. 



In the peninsula to the north of Auckland comparatively recent 

 basaltic rocks cover a large area. The cones still retain a perfect form 

 in many cases, and the lava flows are but slightly decomposed on the 

 surface. Sections show a complete identity of the rocks with those of 

 Auckland. They belong to the same class, and probably to the same 

 period of activity. 



From this rapid and general survey it will be noticed that the order 

 of events in the volcanic history of the North Island appears to me to 

 have been as follows : — 



1. Eruption of andesitic rocks at Coromandel Peninsula, Waita- 

 kerei, Barrier Island, Whangarei, and elsewhere in the north. 



2. Extensive eruptions of rhyolitic rocks over a wide area. 



3.' ^firuptions of andesitic rocks in the central area and perhaps at 

 Mount Egmont. 



4. Basaltic eruptions in the Waikato region and at Auckland. 



5. Renewed activity in the Tongariro region, with fresh andesitic 

 eruptions. Similar activity at White Island and at Tarawera. 



In this summary I have omitted all reference to the eruptions 

 which formed Pirongia and Kerioi, as I know of no criteria that give 

 a clue as to the relative age of such eruptions, though the fact is perhaps 

 suggestive that their composition and structure is very similar to some 

 of the basic rocks of Post-Miocene age at Dimedin. 



In this brief survey no reference has been made to occurrences of 

 volcanic rocks at Hick's Bay, East Wellington, and some other localities. 

 This is due to the fact that I have had no opportunities of examining 

 rocks from these areas. 



Recent collections made by Mr. R. Speight on the north side of 

 Ruapehu have included specimens of hornblende hypersthene andesite. 

 The hornblende is abundant, and much browner and more pleochroic 

 than in the Mount Egmont rock, and the hypersthene is very abundant. 

 A similar rock occurs at A Taura, a hill 5,000ft. high, between Ruapehu 

 and Ngauruhoe. This is possibly the rock referred to by Hutton. 



