THE ACTIVE VOLCANOES OF NEW ZEALAND 697 



Hauraki Peninsula, andesites followed by rhyolites. Probably 

 the andesites extending north of Auckland up to North Cape were 

 contemporaneous with those mentioned. The important gold 

 veins of the Waihi mines are connected with this period of eruption 

 as a later phase of the activity. 



The great volcanic plateau occupying the central portion of 

 North Island consists largely of rhyolite and pumice with the later 

 extrusions of andesite and related rocks breaking through the rhy- 

 olites. The first evidence of the activity which produced the 

 plateau is found in the rhyolite gravels of the Miocene, but the 

 main eruptions are believed to be of Pliocene age because much of 

 the pumice is found resting on early Pliocene strata and some is 

 interbedded with them. The earliest igneous rocks of this plateau 

 are, therefore, rhyolite and the latest andesite. As to the source 

 of these acid rocks, there are factors which point to the Taupo 

 area as the center of the eruption. While the writer did not have 

 the opportunity of visiting Lake Taupo, he is convinced, after 

 visiting other lakes in this region and reading descriptions of the 

 Taupo basin, that these larger lakes in the central portion of the 

 island are old craters modified by faulting. There is so much in 

 common between such depressions and many of those of crater origin 

 in the Hawaiian Islands that their origin can scarcely be in doubt. 



The early andesite eruptions of Ruapehu, Tongariro, Egmont, 

 Edgecombe, and related volcanoes occurred in the Pliocene, while 

 the basanites of the Auckland area are probably of Pleistocene age. 



PETROGRAPHICAL PROVINCES IN NEW ZEALAND 



There is such a close relationship between the rocks of the 

 Ruapehu- White Island and Egmont- Auckland zones that they may 

 be justly regarded as belonging to one province. The rocks of 

 Mount Egmont consist of hornblende-andesite and hornblende- 

 augite-andesite; those of the Auckland region of basanite, poor 

 in nepheline and probably lacking in this mineral in some cases; 

 those of Ruapehu of augite-hypersthene-andesite ; and those of 

 White Island of hypersthene-andesite. 



On the Coromandel Peninsula there were first eruptions of 

 andesites of various types followed by rhyolite and these again by 



