184 



CAPT. F. W. HUTTON ON THE 



of Eotomakiriri and the White Terraces. Between it and Mt. 

 Tarawera a new lake has been formed, with precipitous sides, about 

 a mile in length and a quarter of a mile broad, but of irregular 

 outline ; whether this lake is connected with Rotomahana or not, I 

 do not know. Between the northern end of the new lake and the 

 southern end of the western fissure on Mt. Tarawera is another 

 crateriform hollow, which is not connected with the lake or with the 

 fissure. South of Rotomahana, in the valley of the Haumi, are the 

 Okaro craters. There appear to be six or seven of them, situated on 

 a line which curves round to the south towards Kakaramea. These 

 are not connected by a fissure. They are flat-edged, more or less 

 cylindrical holes, in which the surface rocks can often be seen, and 

 none of them has thrown up a cone more than a few feet high. 

 The first, or southern crater, is two miles from Kakaramea and 

 has been estimated by Mr. Percy Smith at 250 yards long by 

 100 wide and 120 deep ; the sides, however, are falling in, and it 

 will soon become conical. The third crater, called the Black 

 Crater, is divided into two by a narrow ridge of old rock which has 

 been left ; it is situated at the foot of a low hill, and when seen 

 from a distance, in certain directions, this hill looks like a scoria 

 cone. Irom this deceptive appearance it has been called Mt. 

 Hazard ; but the hill is part of the old surface, although of course 

 covered, like the rest of the neighbourhood, by several feet of ash 

 and stones. 



Products of the Eruption. 



The materials ejected are of two kinds, augite-andesite and 

 rhyolite, and each is in both the compact and the vesicular state. 



The Augite-andesite, when compact, is greyish black, vesicular in 

 places, and with opaque, white, angular fragments of decomposed 

 rhvolite or felsite. It is an andesite lava that has overflowed 

 and included rhyolite; S. G. = 2*67. The ground-mass is a brown 

 glass with magnetite globulites, and it contains numerous felspar 

 laths which show no fluxion-structure, except that they are arranged 

 round the white rhyolite fragments parallel to their sides. One 

 slide showed a quartz crystal broken across and faulted. In the 

 vesicular state it is black scoria, very opaque ; but in thin edges 

 near the vesicles it is seen to be a yellowish-white glass full of glass- 

 inclusions, globulites, and other impurities. In contains fragments 

 of quartz as well as of rhyolite. I saw one broken crystal with 

 aggregate polarization, probably partially decomposed hornblende. 



The Rhyolite is of two kinds. The first is a pale-grey, stony rock 

 with abundance of quartz grains, fragments of a white mineral like 

 kaolinized felspar, and some pyrites. The ground-mass is opaque, 

 but when very thin is seen to be crypto-crystalline, probably a 

 devi trifled glass. It contains abundance of quartz and fragments 

 of decomposing sanidine with aggregate polarization in which 

 occasional traces of Carlsbad twinning are recognizable. There is 

 also a green mineral with aggregate polarization, probably horn- 

 blende, and magnetite or ilmenite. With reflected light the base is 



