366 Transactiom. — Geology. 



formation, but are all portions of the rliyolitic rocks adjacent — 

 a fine-grained tuff and coarse-grained brecciated tracbytic rocks 

 being plentiful. In the Wairoa, however, we find both scoria 

 and the cross-grained trachyte just alluded to ; while on the 

 eastern end the principal solid material is composed of a basic 

 scoria, in the form of lapilli. Eeturning now to the examina- 

 tion of the mud and ash, we find that the deposits at Okaro, 

 Wairoa, Tikitapu, and Tauranga are very similar in appearance, 

 being composed very largely of silica, both in the glassy solid 

 crystalline form and as sinter ; together with a small but vary- 

 ing proportion of scoria. Coming next to the deposit at Matata 

 and Whakatane, we find the silica in the same forms, but the 

 scoria has increased considerably in proportion. Advancing 

 still further eastward to Opotiki, we find the same characteristics, 

 but the scoria has still further increased in its proportion to the 

 uncombined silica.* Now, if we turn to the analysis we have 

 made of the materials obtained from the places mentioned, we 

 find that they bear out the results of our optical examination. 

 Clearly the ash fi'om Okaro, Wairoa, and Tauranga are of the 

 acidic group, while those from Whakatane and Opotiki are more 

 nearly approaching the basic form. Again, the scoria obtained 

 from Wairoa, and also from the southern end of the eruption, 

 are undoubtedly basic, and have been thrown out in exceedingly 

 large quantities, viewed from the amount and composition of 

 the eastern deposits. Now, hitherto we have had the whole of 

 the rocks of this region placed in the acidic group, and certainly 

 no large mountain masses of a basaltic character could well 

 escape the practised eyes of Von Hochstetter, or the members 

 of the Geological Staff of our Colony. We are therefore forced 

 to the conclusion that large quantities of basaltic scoria were 

 ejected fi'om the Tarawera volcano, or mountain, at the earlier 

 stages of the eruption on the morning of the 10th of June. 

 This is fully borne out by the numerous eye-witnesses, who 

 unanimously speak of cohimns of fire rushing up from the 

 newly-formed craters, and masses of fire bursting and falling 

 back and around the sides of the mountain. That there was 

 no outflow of molten lava actually discernible after the night in 

 question is accountable by the enormous rush of high-pressure 

 steam carrying off the molten mass in a fine state into the air, 

 where it was carried away by the strong south-west wind which 

 had now commenced to blow, or by benig covered up by sub- 

 sequent deposit of ashes. 



We see from the foregoing that wo have had two distinct 

 eruptions, the one hydrothermal, the other volcanic, throwing 



• The deposit found on the shores of Rotoiti contains large quantities 

 of fine scoria, and as the mountains are approached this increases in 

 quantity and the size of particles, until, on the top of Ruawahia, scarcely 

 anything else is found. 



