HuTTON. — Geology of the Island of Falcild. 113 



Art. XVI. — On the Geology of the Island of Palcihi. 



By Captain F. W. Hutton, F.G-.S. 



Plate V. 



{Read hefore tJie Auclcland Institute, Ztli October, 1868.] 



The Island of PakiM lies between tlie Island of Punui and the mainland, at 

 the north-west end of the Pirth 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 hiU 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 

 Palaeozoic period.* 



The north-eastern extremity is composed of hard blue and green sand- 

 stones, brecciated in places, and much jointed, the fissiires 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 Y.) 



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. — Ed. 

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