apbil — sept. 1859.] the Province of Auckland. 149 



The Auckland Volcanic District. 



The Isthmus of Auckland is completely perforated by volcanic 

 action, and presents a large number of true volcanic hills, which, 

 although extinct and of small size, are perfect models of volcanic 

 mountains. These hills — once the funnels out of which torrents 

 of burning lava were vomited forth, and afterwards the strong- 

 holds of savage cannibals — are now the ornaments of a happy land, 

 the home of peaceful settlers, whose fruitful gardens and smiling 

 fields derive their fertility from the substances long ago thrown 

 up from the fiery bowels of the earth. 



My Geological Map of the Auckland District contains no less 

 than sixty points of volcanic eruption within a radius of ten miles — 

 the variety of which, together with the regularity of their forma- 

 tions, gives very great interest to this neighbourhood. The newer 

 volcanic hills round Auckland are distinguished from the older 

 ones in the interior, not only by their age, but by the different 

 character of their lava — the older being trachytic, while the Auck- 

 land are all basaltic. I have not yet mentioned the difference be- 

 tween Trachyte and Basalt. I will therefore say a few words in 

 explanation. The difference consists in the minerals of which the 

 rocks are composed. Trachyte is composed of a mixture of glassy 

 feldspar (Sanidin) and hornblende: obsidian and pumice-stone 

 are the usual concomitants of trachytic lava. Basalt consists of a 

 minutely- crystalline mass of feldspar mixed with augit : an admix- 

 ture of greenish grains of Olivin is characteristic of basalt. 



In order to gain a clear idea of the history of the Auckland 

 Volcanoes, we must suppose that before the period in which the 

 Auckland Isthmus was slowly raised above the level of the sea, a 

 submarine volcanic action was already going on. The products of 

 this submarine action are regular beds of volcanic ashes, which 

 form highly interesting circular basins with strata always inclining 

 from within, outwards. You will at once remember several strik- 

 ing examples which I can mention — as the Pupuki Lake on the 

 North Shore ; Orakei Bay in the Waitemata ; Geddes's Basin 

 (Hopua) at Onehunga; and the tidal basin (Waimagoia) at Pan- 

 mure ; — Pupuki Lake, believed to be bottomless, has been ascer- 

 tained by Captain Burgess (who kindly sounded it at my request) 

 to be only 28 fathoms. I call those basins and similar forma- 



