Hurroy.—Geology of the Island of Pakihi. 113 
Art. XVL—On the Geology of the Island of Pakihi. 
By Captain F. W. Hurron, F.G.S. 
Plate V. 
[Read before the Auckland Institute, 5th October, 1868. ] 
Tux Island of Pakihi lies between the Island of Punui and the mainland, at 
the north-west end of the Firth of the Thames. It is rather more than a 
mile in length and a third of a mile broad, the longer axis lying about 
north-east and south-west. Both extremities of the island are high, the 
north-east end forming a conical-shaped hill 433 feet high, known as 
“ Pakihi Hill," while the centre is a low, fertile valley. 
The whole of the rocks found on the island belong to the Upper 
Paleozoic period.* 
The north-eastern extremity is composed of hard blue and green sand- 
stones, brecciated in places, and much jointed, the fissures of the joints 
being filled with peroxide of iron. These sandstones dip about 40° W., and 
are overlaid by a series of soft, blue, sandy slates, 1,000 feet thick, containing 
blocks of the harder sandstones, which lie under them. They decompose 
very easily to a soft reddish-yellow clay, in which state they are almost 
always found at the surface. Near the upper part a band about six feet 
thick occurs, of a friable green schistose rock, containing small rounded 
pebbles. (See Plate V.) 
This series is covered by a mass of red or brown jasperoid slates, 
containing large quantities of manganese ore. These jasperoid slates are 
more than 1,300 feet thick. The manganese occurs in numerous bands, 
about an inch thick, generally running parallel to the cleavage of the 
slates, but occasionally at right angles with it. The ore appears to be 
almost entirely psilomelane, little if any pyrolusite being mixed with it. 
On the west coast large quantities could be obtained at a very small 
expense. 
Across the centre of the island runs a fault, which throws up the 
south-western portion about 500 feet, again exposing the series of soft 
sandy slates. The dip, however, is increased to about 70° W., which soon 
brings the jasperoid slates down to the sea level, and the whole of the 
‘south-west portion of the island is composed of them. 
* Perhaps also partly Triassic.—Ep. 
15 
