106 president's address — SECTION c. 



and indicates that th© present igneous activity in the North Island 

 commenced in the Tertiary period. Th:'s was emphasized in Mar- 

 shall's (iy08) useful summary of the volcanic geology of the centre 

 of the North Island, to which refeTenc© should be made. Mentiorn 

 should also be made of Clarke's (1912) d'Cscription of the 

 agglomerates, &c., near New Plymouth. . In the South Island, 

 Speight (1917) has shown that succeeding the C'retaceous 

 rhyolitic eruptions of Lyttleton, there was in pTobably Late 

 Trtrtiary times an outpouring of basalt flows, building up huge 

 cones at Lyttleton and Akaroa, associated with radiating trachytic 

 dykes of an alkaline character. Between these, a third volcanic 

 centre was formed at a somewhat later period, and without a 

 radiating series of dykes. Thus was produced a great volcanic 

 island some di..tance off shore, which being subsequently encroached 

 upon by the prograding shore, has become Bank's Peninsula. In 

 oppooition to Haast's view that the harbours of Lyttleton and. 

 Akaroa were explosion craters, Speight shows that they more prob- 

 ably result from the drowning of valleys which had cut back into 

 th© centres of the great volcanoes. 



The volcanic rocks of the Dunedin district rest upon an irregular 

 surface of Middle Tertiary beds, and overstep thence until they 

 rest upon the basement schists. They consist of basalts, tracliy- 

 doleriles, and a variety of more alkaline trachytes and phonolites. 

 Marshall's (1914) account of the wonderful succession of flows at 

 North OtagO' Head is a notable addition to his earlier generali-'ed 

 description of the whole area (1906), and leads to th© interesting 

 conclusion that the series of flows are derived from an essexitic 

 (trachydolerite) magma, which was injected at several epcchs into 

 subordinate magma-reservoirs, from which, after differentiation, 

 the basalts and m.ore alkaline lavas were ejected. Detailed studies 

 of other portion?, of the district have been mad© by Cotton (1909) 

 and Bartrum (1913). These investigations ar© being extended by 

 the writer and his students, and indicate the great complexity cf 

 the sequence of events in this region. 



Other small areas of Cainozoic volcanic rocks exist, but have 

 not been investigated during the past decade. 



Nor has there been carried out in this period any work of note 

 on the Recent volcanic action in New Zealand, except Moore's 

 interesting account of an ascent of Ruapehu and Ngauruhoe 

 (1917), and the detailed survey of Mt. Egmont by Morgan and 

 Gibson, which awaits publication. The older work, which 

 was summarized by Marshall (1908, 1912), Speight (1908), 

 and Park (1910), leads to the interesting conclusiom 

 that the main centres of volcanic activity in the North 

 Island lie on a line passing in a north -easte.rly direction from 

 Ruapehu, through Nga'iruhoe, Tongariro, Pihanga, Tauhara, 

 Mt. Edgecumbe, and White Island, which is nearly straight, and 



