HuTTON. — On tlie Basin of Te Tarata, Bolomahana. 107 



only half filling the basin, and eyidently sinking. In abont an hour's time 

 the basin was empty, and in half an hour more the water had receded about 

 10 feet down the central pipe, where it remained during the rest of our stay. 

 The wind was light and westerly. 



This phenomenon appears to be of not very frequent occurrence, as Mrs. 

 Spencer, of Tarawera, informed me that, although she had visited the spring 

 some fifty times, she had only once seen it empty. A few notes, therefore, 

 on the shape and dimensions of the basin will not be uninteresting. 



After the water had descended into the pipe we were enabled with safety 

 to go down into the basin, and approach close to the edge of the j)ipe, and 

 walk all round it. Unfortunately I had no means of measuring it accurately, 

 and the following dimensions are partly from pacings, and partly estimated. 

 (See Plate Y.) 



The basin is situated about eighty feet above the level of the lake, and 

 lies in a crateriform hollow cut out of the hill behind it. This hill is com- 

 posed of felspathic^tufa, decomposed into yellow and red clays where acted 

 upon by the steam and gases exhaled from the spring. It is a slight 

 admixture of these red clays with the siliceous sinter that gives to the 

 terraces of some of the springs their beautiful pink colour. 



The sinter-basin is irregularly circular, and about twenty-six yards in 

 diameter and five deep. The upper lip is smooth and fiat, and from 

 four to six feet broad. The sides and bottom of the basin are very 

 irregular and rough, and apparently fissured, as steam escapes in two or 

 three places on the western upper edge of the basin. The north and west 

 sides are much steeper than the others, the easiest point of descent being 

 on the east. The pipe is placed a little to the west of the centre of the 

 basin, and is irregular in shape ; the west and south sides being circular, 

 while the north-east one is flat. The average diameter is about eight feet, 

 and the sides are quite perpendicular and smooth. 



The deposit from this spriag is at first soft and granular, like very fine, 

 fresh-fallen snow, and the foot sinks in it to a depth of about a quarter of 

 an inch. In time it hardens and becomes more compact, probably partly 

 from the pressure of other layers, and partly from the infiltration of fresh 

 siliceous matter. The microscopical structure of the freshly-deposited 

 suiter is extremely peculiar, and deserves a careful examination. It is, for 

 the most part, composed of small elongated particles very variable in shape, 

 but presenting, generallj^, the appearance of small sticks, and is altogether 

 much more like organic than mineral matter. These sticks, of which 

 I have figured a few (see Plate Y.), are about 0*002 inch in length, and 

 0"0002 inch in breadth, and are mixed with larger angular grains of 

 transparent silica, but without any crystals or crystalline particles. 



