NOXKS AND (.niKlillOS. 
195 
the usuixl concomitants of tracliytic hiva. Basalt consists of a minutely crys- 
talline mass of felsjiar mixed with augitc ; an admixture of greenish grains of 
olivim^ is characteristic of basalt. 
lu order to gain a clear idea of the history of the Auckland volcauos, we 
mnst snp))0sc 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 [)roducts of t his 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 t he Waiteniata ; Geddes' Basin 
(Hopua) at Onehunga, and the tidal basin (Waimagoia) at Banmure. Pupuki 
Lake, believed to be bottomless, has been ascertained by Cajjtain Burgess to 
be only twenty-eight fathoms. The excellence of the soil 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 oljserve 
how the shrewder amongst the settlers, without any geological knowledge, 
have picked out these tuU'-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- 
tmuing, 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 
Raugitoto, were formed, and great outflowings of lava took place. Many 
peculiar circumstances, however, prove that those mountains have not been 
Durning all 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 diiferent ages. Tiie 
result of the earliest submarine eruptions is a tuff-crater. The Paumui-e-road 
passes through the tuff-crater, and the cutting through its brim exhibits beau- 
tifully the charactei-istie outward-inclination of the beds of ashes, elevated from 
their former horizontal levels by the erujjtions, which threw up the two minor 
crater-cones soutli 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 Liu," the 
eculiar difference in the colour on the road, suddenly changing from red to 
lack, where the road leaves the older and more decomposed lava-streams of 
Mount AV^eUington. The farmers have been able to avail themselves of the 
the decom|joscd lava-surface, which is now 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, Moimt Smart, Mount Wellington, 
&c., are the result of great bubbles iu the lavarstreams, occasioned by the 
generation of gases and vapour as the hot masses rolled onward over marsliy 
plains. These bubbles broke down on their thimiest part — the roof; hence tlie 
way into the caves is always directly downward. 
