NEW ZEALAND. 443 
of feldspar, besides a few small grains of chrysolite. Its colour is dark 
bluish-gray or grayish-black, from which fact they are generally 
designated the Black Rocks. 
‘‘ BLACK ROCK,’’ BAY OF ISLANDS. 
Other similar islands lie not far distant up the same portion of the 
Bay, near the mouth of the Kirikiri River, and the whole appear to 
have had a simultaneous origin, as may be inferred from their unifor- 
mity in height and other characters. The siliceous hardness of the 
rock of Tipuna Bay, and also of Parua, to the southward, is probably 
due, in some way, to the heat of the injected basalt, and the silica 
which might have been dissolved at the time by the heated waters 
within and around these rocks. ‘The quartz veins and chloritic beds 
may have had the same origin. 
The volcanic cones of this part of New Zealand he twelve to 
sixteen miles to the westward, in the district of T'aiamai. ‘There 
are here four regular cones, standing upon the same broad plain, be- 
sides regions of hot springs and sulphur exhalations. 
The largest of the cones, called Ahuahu, stands about nine hundred 
feet above the plain. It has very evenly sloping sides, inclined at an 
angle of thirty-five or forty degrees, and terminates above in a narrow 
truncated summit. Its regularity and perfection of form lead us to 
infer that its fires were gradually extinguished, after a period in which 
cinders were quietly thrown out. 
Mount Turoto is much smaller, its height not exceeding three hun- 
dred feet. ‘The sides are more sloping than those of Ahuahu; the 
opening of the crater is very much broader, and has an undulated out- 
line, with one side a little the highest. From a neighbouring emi- 
nence we had a glimpse of the interior of the crater, and of the large 
forest trees, which thrive well in the moist volcanic soil. 
Poerua stands farther to the south, and is about twice the height of 
Turotu. It appeared in the first view to be an unbroken cone, perfect 
in symmetry; its smoothly sloping sides were overgrown with ferns, 
among which there was rarely a shrub to be seen. Farther to the 
westward the view changed. <A deep gorge was seen to intersect the 
western side of the cone, exposing the interior of the crater, as shown 
in the following sketch. On the ascent, we passed over a fine black 
