XOTES AND QUERIES. 



195 



tlie usual concomitants of tracliytic lava. Basalt consists of a minutely crys- 

 talline mass of felspar mixed with augite ; an admixture of greenish grains of 

 olivine is characteristic of basalt. 



In order to gain a clear idea of the history of the Auckland volcanos, 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 abeady 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. Several striking examples can be mentioned, as the Pupuki 

 Lake on the north shore, Orakei Bay in the Waitemata ; Geddes' Basin 

 (Hopua) at Onehunga, and the tidal basin (Waimagoia) at Panmui-e. Pupuki 

 Lake, believed to be bottomless, has been ascertained by Captain Burgess to 

 be only twenty-eight fathoms. The excellence of the soU of Onehunga and 

 Otahuhu is owing to the abundance of such formations, the decomposed strata 

 of which form the richest soil that can be met with. It is curious to observe 

 how the shrewder amongst the settlers, without any geological knowledge, 

 have picked out these tufp-craters for themselves, while those with less acute 

 powers of observation have quietly sat down upon the cold tertiary clays. 



After the submarine formation of the tuff-craters, the volcanic action con- 

 tinuing, the isthmus of Auckland was slowly raised above the sea, and then the 

 more recent eruptions took place by which the cones of scoria, like Mount 

 Eden, Mount Wellington, One Tree Hill, Mount Smart, Mount Albert, and 

 Rangitoto, were formed, and great outflowings of lava took place. Many 

 peculiar circumstances, however, prove that those mountains have not been 

 burning aU simultaneously, for it can easily be observed that some lava- 

 streams are of an older date than others. In general the scoria-cones rise from 

 the centre of the tuff-craters (Three Kings, Waitomokia, Pigeon Hill near 

 Howick) ; but occasionally, as in the instance of Mount Wellington, they break 

 through their margins. 



The crater system of Mount Wellington is one of the most interesting in this 

 neighbourhood. There are craters and cones of evidently different ages. The 

 result of the earliest submarine eruptions is a tuff-crater. The Panmure-road 

 passes through the tuff-crater, and the cutting through its brim exhibits beau- 

 tifully the characteristic outward-inclination of the beds of ashes, elevated from 

 their former horizontal levels by the eruptions, which threw up the two minor 

 crater-cones south of the road, one of which is now cut into by a quarry. 

 After a comparatively long period of quiescence, there arose from the margin of 

 the first crater system the great scoria-cone. Mount Wellington, from the three 

 craters of which large streams of basaltic lava flowed out in a westerly direc- 

 tion, extending north and south along the existing valleys of the country, one 

 stream flowing into the old tuff-crater, and spreading round the bases of the 

 smaller crater-cones. The larger masses of these streams flowed in a south- 

 westerly direction towards the Manukau, coming into contact with the older 

 and long-before hardened lava-streams of One Tree Hill. The traveller on the 

 Great South Road will observe about one mile east of the "Harp Inn," the 

 pecuHar difference in the colour on the road, suddenly changing from red to 

 black, where the road leaves the older and more decomposed lava-streams of 

 Mount Wellington. The farmers have been able to avail themselves of the 

 the decomposed lava-surface, which is noAV beautifully grass-covered, but not of 

 the stone-field of the newer streams from Mount Wellington and Mount Smart. 



The caves at the Three Kings, Pukaki, Mount Smart, Mount Wellmgton, 

 &c., are the result of great bubbles in the lava-streams, occasioned by the 

 generation of gases and vapour as the hot masses rolled onward over marshy 

 plams. These bubbles broke down on their thinnest part — the roof ; hence the 

 way into the caves is always directly downward. 



