35 



of the lake ; and so on to Tarawera, Mount Edgecumbe, Whale Island, 

 and White Island the last being a very active centre. 



The foundation of these volcanoes was laid during the middle and 

 latter part of the Tertiary era on underlying sedimentaries of early 

 Mesozoic age, but the extrusive processes became most active during 

 the Early Pleistocene and later, the volcanic development being no 

 doubt a manifestation attendant on, though not necessarily a con- 

 sequence of, the elevation of the central portion of the North Island. 

 The deeply entrenched beds of the Rangitikei, Wanganui, and Mokau 

 Rivers, which rise in the vicinity of the volcanic zone, demonstrate 

 this upward movement, and there is biological evidence based on the 

 distribution of plants and animals which suggests that an arm of the 

 sea existed in late Tertiary times right into the heart of the Island, 

 if not actually across it, dividing it into two or more detached 

 fragments, which have been subsequently joined as a result of these 

 elevatory movements. 



The first eruptions of the region were in all probability rhyolitic 

 in character, since there is a widespread distribution of pumice of 

 that nature in Tertiary sedimentary deposits of the surrounding 

 country, as well as lava-flows of the same lithological character over 

 a more restricted area ; but these do not show within the limits of the 

 Park. If they do exist they are completely masked by the later 

 volcanic material, which consists of augite-hypersthene andesites and 

 hornblende-hypersthene andesites, the former being far in excess of 

 the latter in geological importance. During the last stages a little 

 olivine appears, indicating a more basic facies. Although the ande- 

 sites form the most recent rocks of Ruapehu and its associated cones, 

 there is an extensive deposit of pumice over the whole central area 

 of the Island, forming a thin veneer in most places, but thick drifts 

 along the watercourses and at times on the mountain-slopes. The 

 recency of this pumice covering is shown not only from its position on 

 the top of all other surface material, but from its containing charred 

 logs in such numbers and in such positions as point to the destruction 

 of the forests at a quite recent date. The source of this pumice is 

 doubtful, but it has been suggested that it came from Taupo as 

 the result of a paroxysmal explosion which formed the basin now 

 occupied by the lake. The general evidence, however, points to tec- 

 tonic movements as being responsible for the formation of this basin. 

 The earthquakes recently recorded from that district clearly indicate 

 that the crust in its vicinity has not yet reached a condition of 

 stability. R< SPEIGHT. 



THE PLANT-LIFE OF THE TONGARIRO NATIONAL PARK 

 AND ITS ENVIRONS. 



The area here dealt with includes the loftiest part of the North 

 Island, together with its extension to the Main Trunk line from 

 Waiouru to Waimarino. Nothing is said about the forest associa- 

 tions, since such do not differ greatly from those in certain other 

 parts of the North Island. What follows is devoted to the flora 

 and vegetation of the open country, nearly all of which lies at an 

 altitude of more than 3,000 ft. 



