THE GEOLOGY OF AUCKLAND. 
41 
system the great scoria cone of Mount Wellington, from wnose 
three craters large streams of basaltic lava flowed out in a 
Westerly direction, extending North and South along the 
existing valleys of the country, one stream flowing into the old 
tuff-crater, and spreading round the bases ofthe 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 ofthe “Harp of Erin Inn” the peculiar difference in the 
colour on the road, suddenly changing from red to black, whet e 
the road leaves the older and more decomposed lava streams of One 
Tree Hill and passes onto the new and undecomposed lava streams 
of Mount Wellington. The farmers have been able to avail 
themselves of the decomposed lava surface, which is now 
beautifully grass covered, but not of the stonefield of the newer 
Mount Wellington and Mfount Smart streams. 
The Caves at the “ Three Kings,” Pukaki, Mount Smart, 
Mount Wellington, &c., are the result of great bubbles in the 
lava streams—occasioned probably by the generation of gases 
and vapour as the hot mass rolled onward over marshy plains. 
These bubbles broke down on their thinnest part the roof— 
and the way into the caves is always directly downwards. 
Examples of every gradation may be seen—from the simple 
tuff-crater without any cone, to those which are entirely filled 
up by the scoria cones. Especially interesting are those which 
may be said to represent the middle state, in which there is a 
small cone standing like an island in a large tuff-crater, and 
surrounded by either water or swamp. Perhaps the most perfect 
specimens of this kind occur at Otahuhu and near Captain 
Haultaiifs, a map of which, from actual measurement, has been 
prepared by Mr. W. Boulton. You need not be alarmed when 
I tell you, that even the very spot on which we are assembled is 
the centre of an old tuff-crater, from which fiery streams, once 
issued, and which has thrown out its ashes towards the hill on 
which the barracks stand.—In order to account for these various 
shapes, it must be borne in mind that the cones of scoiia were 
once higher, but on the cessation of volcanic action they sunk 
down in cooling, and some entirely disappeared. 
