172 BEPORT— 1891. 



now described is the only one on Euapehu. No doubt it is the 

 only one in activity, but the great ice-field may cover a number 

 of craters the top walls of which are represented by the steep 

 ridges of lava rock which in a measure encircle the ice on the 

 top of the mountain. The great broken-down crater where the 

 Whangaehu Eiver takes its rise adjoins the lake on the eastern 

 side, and it may be that other craters in the direction of Te 

 Heuheu Peak are simply filled with ice, just as the craters in 

 the northern portion of the range are filled with water. 



Most of the rocks forming the upper parts of the cones of this 

 range of volcanoes belong to the basic and intermediate lavas, 

 whilst the slopes running from the mountain are all acidic 

 trachytes, and these appear to underlie as a great sheet the 

 whole of the plain extending from Euapehu to Eunanga, on the 

 Napier-Taupo Eoad. On the west side of Euapehu there is a 

 very curious line of conical hills running across the plain from 

 Euapehu in a north-west direction for several miles. These 

 hills are all trachytic in structure, and they appear at intervals 

 of about 200 yards. Their height is from 150ft. to 200ft. 

 There is no trace whatever of a crater on any of them. 

 Probably they are simply the result of blistering on a lava- 

 flow, just as we see blistering take place when melted lead is 

 poured upon a damp and enclosed surface. 



Basalt, phonolite, pitchstone, and tachylite are- found in 

 abundance in Euapehu, especially on the east side by way of 

 the Whangaehu Eiver. Extensive flows of phonolite are met 

 with at a height of about 6,000ft., great slabs 5ft. or more in 

 length and varying from an inch to two inches in thickness 

 being common. The pitchstone is well seen in a spot named 

 Waterfall Gully, on the east side of the mountain, and the 

 basalt on the north-east in the direction of Te Heuheu Peak. 

 The tachylite is only found in nodules among the lapilli on the 

 lower spurs of the cone. Along some of the northern slopes 

 there are vast deposits of a heavy pumice of a bouldery cha- 

 racter. This, it seems to me, must have come from the crater- 

 lakes of Nga-puna-a-Tama, as the line is traceable in a kind of 

 fan from these lakes in a south-east direction. 



5. Ttvisted and Broken Crystals of Tourmaline. 

 By Professor Jack. 



