698 E. S. MOORE 



hypersthene-andesite. It is probable that the great rhyolite 

 extrusions of the central plateau were contemporaneous with those 

 of the Coromandel Peninsula, and that the early andesite extrusions 

 of this region did not occur in the plateau area. There are dacites 

 in both areas. 



Park considers that there are two other petrographic provinces 

 in New Zealand of late Miocene or early Pliocene age, these being 

 found on the Otago and Banks peninsulas. 1 In the former penin- 

 sula the rocks consist of an earlier series of phonolite, dolerite, 

 trachydolerite, andesite, basalt, and basanite; and a later series, 

 erupted on the eroded surface of the first, consisting of basalt with 

 probably andesite and phonolite. Cutting the lavas of the first 

 series are dikes of nephelite-syenite, augite-dolerite, and tinguaite. 

 Professor Marshall, who has made a detailed study of this area, 

 states that no regular order of eruption and no definite system of 

 differentiation in these various rocks have, so far, been recognized. 



On Banks Peninsula there was a period of rhyolite eruption 

 followed, after considerable erosion, by andesites and basalts. 



From the evidence presented there does not seem to be any 

 regular order of eruption followed by rocks of the various types, 

 except that in practically all cases there is a tendency for the volcan- 

 ism to cease with the eruption of intermediate rocks, as andesites. 



RUAPEHU, NGAURUHOE, AND TONGARIRO 



These three large volcanoes are located near the center of North 

 Island at the southern end of the rhyolite plateau. Their craters 

 lie along a direct line, within a distance of less than fifteen miles, 

 and if this line be projected northeastward it will pass also through 

 Pihanga and Tauhara, volcanoes now extinct; then through 

 Tarawera, Edgecombe, and White Island. Ngauruhoe is situated 

 between the other two and almost on the side of Tongariro, in 

 such a way as to indicate that it has arisen in the later stages of 

 Tongariro as a subsidiary cone to this great volcano. 



The rocks of all three of these volcanoes are similar, and consist 

 of augite-andesite with augite-hypersthene-andesite. The early 

 activity produced extensive flows of these rocks followed by 



1 Park, op. cit., p. 147. 



