281 



to be renewed by a repetition of tbe same process. The store built up of 

 these incrustations is thus rapidly encroaching on the lake. 



In the vicinity of the lake, and chiefly at a few feet above the water's 

 edge, are round holes, in which boiling mud is kept in violent agitation by the 

 escape of steam, and at the interior end of the lake occasional outbursts of 

 boiling water take place, rising to the height of several hundred feet. The 

 lai'ge masses of sulphur which are so frequently brought from White Island, 

 are chiefly obtained from the vicinity of these geysers, but a considerable 

 quantity also occurs as detached masses among the tufa. It is evidently 

 deposited by the vapours that escape from the fissures, and it is doubtful if it 

 could be obtained in sufficient quantity to have mercantile value. 



When we take into consideration the great depth of the sea around the 

 island, which is quite out of soundings according to the Admiralty survey, and 

 the structure of its rock foi'mation as above explained, it is evident that the 

 present island must be the summit of a deeply submerged conical mountain ; 

 also, that the interior lake of hot water, in former times, stood at a much 

 higher level, which was lowered as the sea waves efiected a breach in the 

 outer wall. 



The overflow from the lake at the present time escapes by a narrow 

 watercourse, which is being i-apidly filled up by the incrusting deposits. We 

 may expect, therefore, that in the course of time the damming back of the 

 o\itlet will again permanently raise the level of the lake, but there appears to 

 be very little doubt that, apart from all such causes, the water is liable to the 

 rapid fluctuation of level which is characteristic of a geyser lake. I may 

 remark, that I observed no signs of marine or beach drift within the crater 

 wall, such as must have existed if the island had been undergoing process of 

 elevation. On the other hand, the evidence seems to point to a steady sub- 

 mergence of the volcanic cone, the encroachment of the sea on the interior 

 lake being prevented by the continual heaping up of the beach, thus keeping 

 the sea water on the outside from mixing directly with the hot mineral waters 

 of the lake. 



We are thus led to the conclusion that AVliite Island is the top of a sub- 

 merged volcanic cone, built up during successive eruptions which took place in 

 the atmosphere. Such volcanic rocks are naturally liable to undergo chemical 

 change, and especially so if bi-ought in contact with sea water, which, in this 

 case, must permeate every part of the submerged mass. The heat generated 

 by this chemical action is probably quite sufficient to give rise to the volume 

 of steam, the constant escape of which is the only sign of supposed volcanic 

 activity which the island now exhibits. 



From the accompanying analyses it will be seen that the greater part of 

 the deposits formed by the thermal waters on White Island are calcareous 

 sulphates, and this, taken in conjunction with the large proportion of free 



2o 



