Hurton.—On the Basin of Te Tarata, Rotomahana. 107 
only half filling the basin, and evidently sinking. In about 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 pipe, 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 V.) 
The basin is situated about eighty feet .above the level of the lake, and 
lies in a erateriform hollow cut out of the hill behind it. This hill is com- 
posed of felspathie 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 flat, 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 cireular, 
while the north-east one is flat. The average diameter is about eight feet, 
and the sides are quite perpendieular and smooth. 
The deposit from this spring 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 - 
sinter 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, generally, 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 V.), are about 0:002 inch in length, and 
0:0002 inch in breadth, and are mixed with larger angular grains of 
transparent siliea, but without any crystals or crystalline particles. 
