174 ME. J. MAET1N ON THE TEEEACES OF EOTOMAHANA. 



overflow would have spread its surface-deposits over the face of the 

 hill, as exhibited in the sinter formations of other hot springs in 

 the district. 



It also appears quite evident that the siliceous lining of the great 

 cauldron could not have been deposited until the process of excava- 

 tion was nearly complete, and that the solid precipitous walls, the 

 comparatively level floor, and the perfectly level encircling rim must 

 have acquired stability of form before the deposition of silica upon 

 their surface. 



The extension of the platform in front of the cauldron and the 

 massive walls and basins which characterize the structure suggest 

 to the careful observer the probability that their formation was due 

 to the deposit, in a plastic condition, of the material thus removed 

 from the crater. 



The phenomena of mud volcanoes exhibited at the plateau of 

 Rotokanapanapa afford to the geologist valuable indications of the 

 probable appearance of the Terata cauldron in the earlier stages of 

 its activity. This circular area, of similar size to the crater of the 

 White Terrace, was situated in a hollow of the same hill, a few 

 chains further towards the west, where the continued or intermit- 

 tent action of steam escaping through felspathic tuff had gradually 

 converted the rock into a perfectly level lake of mud and clay. 

 The surface was covered with a semi-liquid layer from which rose 

 a large number of miniature cones and craters varying in diameter 

 from 2 to 20 feet, the former emitting steam, with occasional spats 

 of mud, the latter bubbling and seething like boiling paste or porridge. 

 Around the edge or outer rim of the area the mud was sufficiently 

 compact to form a firm and safe footpath, while towards the centre 

 it became very soft and hot. 



Extending through a narrow outlet over the slope towards 

 Eotomahana, the mud overflow preserved the same uniformity of 

 level until it fell abruptly over a rounded breastwork which was 

 encroaching upon the vegetation on the hill-side ; the surplus water, 

 thick and creamy at first, deposited its solid matter in hollows and 

 upon obstructions, and finally escaped clear through the scrub to 

 the lake. 



If this condition had been succeeded by a gradual increase of 

 thermal activity, it seems but reasonable to suppose that the softer 

 clays around the centres of action would be slowly removed, to 

 accumulate as masses of deposit upon the slopes below. Inter- 

 mittent discharges of siliceous w 7 ater would carry forward streams 

 of plastic clay, which on meeting level ground would spread out and 

 form sweeping curves of low elevation ; this deposit would rapidly 

 harden, as it dried upon the outer surface, into a cement like 

 concrete ; other following deposits resting upon those already laid 

 would form a series of terraced steps. Succeeding streams of 

 water penetrating through surface-cracks would excavate the still 

 soft and plastic interior and redeposit the solid material thus re- 

 moved, in the form of overhanging lips with pendent or stalac- 

 titic fringes, or as smaller intermediate steps, instances of which 



