92 Transactions. 



flank of the Paeroa Mountains parallel to the Tarawera fissure. 

 These vertical scarps are general in the whole district. They 

 are noticeable at Ngatira, on theJRotorua line, where the railway 

 enters the plateau. They are prominent on the Rotorua side 

 of thisTplateau and on the flanks of Ngongotaha, on Tarawera 

 itself, and in the southern portion of the district such scarps 

 are very prominent on the sides of all the streams that cross 

 the railway-line between Mokau and Porootarao. It is evident 

 that these features are most general, and, as in the southern 

 district there can be no doubt that they are due to the resistant 

 nature of the rhyolite, there is no reason why the same explana- 

 tion should not be accepted for Horohoro and its fellows. If 

 these features are due to faulting, it is remarkable that the erup- 

 tion of Tarawera should have occurred in solid rock, midway 

 between two profound adjacent faults parallel to it, for the 

 sides of Tarawera have notably this scarped form. 



The distribution of pumice has long attracted attention. 

 Cussen has suggested>that it was derived from the Taupo basin, 

 for he noticed that the pumice on the west of the lake became 

 coarser as the lake was approached. McKay has, for reasons 

 of a similar nature, stated that eruptions probably took place 

 somewhat to the east of Taupo. He rightly states that the 

 distribution of the pumice is so great that it is almost impossible 

 that it should have been the product of a single volcano. He 

 supposes that many of the vents have afterwards been smothered 

 in the products of other volcanoes. This statement of McKay 

 probably represents as near an approach to exactitude as can 

 at present be made. At the same time, it is reasonable to 

 regard the lake-basins of the volcanic region as areas that have 

 been affected by violent explosions, possibly of a hydrotherma! 

 or perhaps of a truly volcanic nature. That lake-basins can be 

 formed by such explosions we have good evidence in Lake Roto- 

 mahana, and its contours are not strikingly different from those 

 of the other lakes. If the explosion were accompanied with 

 volcanic action and emission of acidic tuff, we have in the present 

 depressions of the volcanic plateau sufficient points of emission 

 to account for the distribution of pumice. The form of Lake 

 Taupo is particularly suggestive of an explosive origin, though 

 its present dimensions do not probably represent merely the 

 area of the exploded depression. Such a cataclysm causes the 

 outlet to be stopped up, and the gathered waters gradually 

 spread over the adjacent lowlands. 



It is noticeable that though the actual melted rock at Tara- 

 wera was andesitic, yet pumice of an acidic nature was more 

 widely dispersed than the andesitic tuff. If this view is correct, 

 the lakes of the volcanic country must be regarded as filling 



