136 Geological Society : — 



Silica, free and combined with soda 50 



Sodium and potassium chlorides 60 



Alkalies, chiefly soda 30 



Sodium sulphate, &c. 10 



Total 150 



The amount of rock-material withdrawn in solution would amount 

 to about 1 tons per day ; observations lead to the conclusion that 

 10 per cent, of the silica would be deposited on the surface covered 

 by the overflow — equivalent to about 120 tons per annum. Then 

 followed the description of the three divisions previously defined, in- 

 cluding such local features as the Giant Buttress, the Boar's Bead, 

 and the Broken Basin — the latter a circular pool 12 feet in diameter 

 and 30 inches deep — the only warm-water basin on the White Ter- 

 race of sufficient depth to be used as a bath. The central portion of 

 the Middle Terrace was distinguished by a series of massive, rugged, 

 and rippled perpendicular steps, many of which exceeded b* feet in 

 height, and were variously ornamented. The margin of the lower 

 plateau was somewhat undefined towards the lake. 



The Author observed that the comparative study of local pheno- 

 mena must precede any attempt to explain the origin of the Terraces. 

 The phenomena of mud volcanoes exhibited at the plateau of Ploto- 

 kanapanapa afford to the geologist valuable indications of the pro- 

 bable appearance of the Terata cauldron in the earlier stages of its 

 activity. These phenomena he described, and arrived at the conclu- 

 sion that the initial activity of Terata was of a similar nature, and 

 that the successive periods which mark the history of the formation 

 of the White Terrace correspond with the increasing activity of its 

 source. Given a crater-lake of seething mud, as activity increased, 

 the outer wall of the crater would occasionally be broken down, and 

 mud streams would be liberated. Such periodical overflows he re- 

 garded as having built up the curious and complex terraced series. 

 This hypothesis he applied in detail, and concluded that deposition 

 and removal combined to produce the great variety of forms which 

 existed. Thermal activity within the cauldron having at length 

 removed the softened rock, the deposition of siliceous incrustation 

 commenced. 



Lastly he gave a short description of the Pink Terrace, and re- 

 marked that by the catastrophe of June 10th the waters of the lakes 

 Kotomakirisi and Rotomahana were drawn into the new fissure at 

 the base of Tarawera, whilst the Terraces were blown away. 



3. " The Eruption of Mount Tarawera." By Capt. F. W. Hutton, 

 P.G.S. 



The paper commenced with a description of the country in which 

 the eruption took place. Prom Tongariro to White Island, in the 

 Bay of Plenty, a distance of 130 miles, there extends a belt, 20 or 

 30 miles wide, abounding in solfataras, geysers, hot springs, <fec, 

 and composed of volcanic rocks, chiefly rhyolite, with some augite- 

 andesite. About the middle of this belt lie the mountain and lake 

 of Tarawera, and two or three miles further south Lake llotomahana, 



