ME. J. MARTIN ON THE TEREA.CES OF EOTOMA.HANA. 175 



can be observed at the white mud craters of Wairakei, near 

 Taupo. 



The comparative study 0 f local phenomena thus appears to favour 

 the theory that the initial activity of Terata was very similar to that 

 of Eotokanapanapa, and that the successive periods which mark the 

 history of the formation of the White Terrace correspond with the 

 increasing activity of its source. 



The hill surrounding Terata being pierced by numerous steam- 

 jets, it is exceedingly probable that a large number around a common 

 centre originally combined to form a crater-lake of seething mud. 

 As activity increased, the outer wall of the crater would be occa- 

 sionally broken down, and escaping mud-streams would be as 

 frequently liberated. These periodical overflows would form by 

 superimposition upon the hill-slopes the foundation of this curious 

 and complex terraced series. The earlier streams moving slowly 

 through the vegetation on the hill-side, spread out upon the level 

 ground at the base, forming that beautiful series of curves previously 

 described as the Cold-water Basins. The excavation of these 

 basins would be easily effected, if, after the induration of their outer 

 walls, running ivater penetrated through surface-cracks before the 

 consolidation of their central mass. 



The central steeps, which rise immediately above these basins, 

 appear to have been built up by the masses of plastic clay, which 

 issued at successive periods as the wall of the crater yielded to the 

 increasing activity. 



The upper platform, with its massive circular outworks, would 

 have been formed as the enlargement of the crater-gap increased to 

 its historic dimensions, and the level surface, including that of the 

 encircling rim, indicates a period when this entire area was in a soft 

 and plastic condition. 



As the eruptive force augmented, and as intermittent geyser- 

 fountains succeeded, the smaller vents within the area would tend 

 to unite in one enlarged vertical tube. The argillaceous contents, 

 reduced to an exceedingly fine state of subdivision, would by pro- 

 longed boiling be removed and replaced by a siliceous cement^ the 

 more compact encircling rim being left entire around the cauldron. 



The numerous tiers of shallow receptacles known as the Upper 

 Series, hot-water basins, or ' cups 7 appear to owe their regular out- 

 lines to the successive waves of siliceous material which overflowed 

 periodically during the excavation of the cauldron. Evaporation 

 would cause this material to harden rapidly from its outer surface, 

 and thus the lines of elevation would be maintained when the softer 

 interior was removed by succeeding currents. Percolation of water 

 through the pores would increase the deposit of silica within the 

 interstices of the mass and further harden the basin-walls. Thus 

 deposition and removal combined to produce that exquisite variety 

 of form which characterized these horizontal lines of deposition. 



The curious depressions upon the Upper Platform are also readily 

 explained upon the hypothesis that the crust of the upper strata of 



