MR. J. MARTIN OX THE TEEEACES OE ROTOMAHANA 



169 



An approximate analysis of the water gave about 150 grains of 

 solid matter per gallon, viz. : — 



gvs. 



Silica, free and combined with soda 50 



Sodium and potassium chlorides 60 



Alkalies, chiefly soda 30 



Sodium sulphate, and other salts 10 



150 



The amount of rock material thus withdrawn in solution by this 

 geyser at its normal rate of discharge would amount to about ten 

 tons per day. Several observations lead to the conclusion that at 

 least ten per cent, of the silica would be deposited upon the surface 

 covered by the overflow. This would be equivalent to about 120 

 tons per year, and give an average deposit over the entire surface 

 of one inch in fifteen years. Upon the upper portions of the 

 structure the deposit had formed as rapidly as one inch in five 

 years upon various objects placed for experiment in the course of 

 the overflow. 



The Upper Platform extended east and west in front of the basin 

 for 130 feet. Its width at the west end was 15 feet, and at the east 

 10 feet. In front toward the centre it opened out into two large 

 shallow basins. The larger (2so. 2 on plan) circular in outline with 

 a diameter of 60 feet, the other (Xo. 3) semicircular, with a curious 

 double outer rim, had a radius of 20 feet, and between them was a 

 slightly depressed channel 4 feet wide. The outer (eastern) portion 

 of the platform was very curiously broken into miniature lakes and 

 islands, with peninsular points and crescented bays. The surfaces of 

 the elevations were smooth, and of uniform level with the rest of the 

 platform and rim of Cauldron (Xo. 1). These small depressions, as 

 well as the hollows of the two basins (Xos. 2 & 3), had the nearly 

 uniform depth of twelve inches. The sides of the elevations and the 

 floor of the depressions were covered with delicate coral-like deposits 

 of exquisite beauty. 



AYhen the platform was covered by the overflow, these numerous 

 and beautiful depressions escaped notice, the whole surface appearing 

 as a level sheet of water, the visitor being cautiously conducted 

 along the narrow path in front of the rock over which the water 

 would be rippling from the Cauldron. 



The double outer rim of Xo. 3 basin enclosed a deep and beauti- 

 fully ornamented crescent, a yard in width at the widest part. The 

 sides and depths were covered with projecting and interlacing points 

 of coral-like sinter, similar in character and disposition to the fleecy 

 masses which were scattered over the basin floor and which 

 promised in time to fill up the entire cavity. 



This seemed to afford strong evidence that the crescent as well as 

 the other depressions could not have been excavated by the same 

 agency as that by which, they were slowly but certainly filling. 



The breach or outer wall of this (Xo. 3) basin formed a wavy 

 semicircle ten yards in extent and about six feet in height, thickly 

 set with rough projecting bosses and mammillary points. 



Q. J. Gr. S. No. 170. N 



