460 Transactions. — Geology. 



vol. xx., art. xlii., of the Transactions, and is well worth perusal. 

 He estimates that the inflow per second from all the rivers 

 flowing into Taupo amounts to 16,483 gallons, and the outflow 

 to 16,230 gallons. Accepting these estimates as generally correct, 

 and taking the dimensions of the lake as already stated, the 

 cubical contents of the lake amount to nearly 100,000,000,000 

 yards, or a hundred and sixty times more than the quantity 

 that is estimated by Mr. Percy Smith to have been thrown from 

 Rotomahana at the time of the eruption in 1886. The daily 

 inflow to the lake at 16,500 gallons per second is 1,425,600,000 

 gallons. At this rate of inflow, and without making anv allow- 

 ance for evaporation, the lake such as it is to-dav would require 

 307 years to fill, and at least 1,200 years to increase the depth 

 300 ft. more, as the surface of the lake would become so largely 

 extended. 



And what has to be said of the Waikato River ? There 

 certainly could have been no Waikato River whilst the lake was 

 filling, for the river is made up of the surplusage of the lake. 

 Mr. Percy Smith, writing in May, 1894, " on the present state of 

 the country immediately round the site of the Tarawera erup- 

 tion," says that " the crater of Rotomahana, which was formed 

 in 1886, and at the bottom of which was a lake 25 acres in ex- 

 tent, had filled up with water from a level of 565 ft. to 985 ft.. 

 or 420 ft. ; and that the lake had grown in dimension from 25 

 acres to 5,600 acres." He points out that Rotomahana had vet 

 to rise 95 ft. before its waters would commence to overflow and 

 clear a channel down to the level of Lake Tarawera and drain 

 off a considerable portion of the present Lake Rotomahana. 

 This lake, with its extended rifts to the north-east and south- 

 west, is separated from Lake Tarawera by " loose incoherent 

 ejecta," and is the counterpart of Lake Taupo, with its north- 

 east rift along what is now the Waikato River bed, and with 

 Pihanga as the highest point of explosion to the south-west. 

 What has taken place in connection with Rotomahana during 

 the past eighteen years enables us to look back to a time when 

 Taupo and district underwent hydrothermal disturbances of 

 much greater intensity than was experienced at Tarawera. It 

 was then that the pumice was spread over the Taupo district, 

 and the lava plateau that is now so extensively covered with 

 volcanic dihris was split in twain and subsidence took place. 

 The raised mass of debris that covers the land along the north 

 end of the lake from the Terrace Hotel to the Spa Sanatorium 

 represents material that has filled up a pail of the original 

 (■lateral rift, which can be traced for many miles down the 

 present Waikato River. 



When the later volcanic disturbances began, the present 



