Marshall. — Geology of North Island. 89 



proof of the statement. Such Pliocene deposits are, however, 

 found in the Hawke's Bay and Wanganui districts. The former 

 district has been described by Mr. Hill,* who mentions pumice 

 and volcanic material in the Upper Pliocene only. From this 

 it appears that the volcanic action which distributed pumice 

 in the Miocene became dormant in the Upper Pliocene, or 

 became extinct, and a new district became active in its place. 



At Wanganui, Parkf has stated that volcanic material is 

 found in the Upper Pliocene only. This agrees with Hutton'sf 

 statement and with that in his geological history of New^Zea- 

 land.§ With these statements my observations entirely agree, 

 and I would add that the lower gravels of volcanic material 

 in the Upper Pliocene at Wanganui contain a much larger 

 quantity of pebbles of Mesozoic sediments and of rhyolites than 

 the higher strata of gravels, which consist almost entirely of 

 andesitic pebbles. This suggests that in the early Pliocene 

 the sediments of the range west of Taupo had not become so 

 nearly obliterated by volcanic ejecta as now, and that the 

 Ongaruhe was then cutting its gorge vigorously through the 

 white rhyolite, while the Wanganui did not have its head- 

 waters obstructed, in bringing gravels from the Kaimanawas, 

 by the huge andesitic masses of Ruapehu and his fellows. Later 

 on, as Ruapehu grew, the source of sedimentary pebbles was 

 cut off, and the steep slopes of Ruapehu yielded more and more 

 material to the streams that coursed down its sides. 



Further north the volcanic cones at Auckland are of extremely 

 recent age. Their lava-streams flowed down valleys that still 

 exist. So recent are the lavas that streams still flow beneath 

 them through the loose scoriaceous matter of their lower surface. 

 In no instance has a stream cut a higher-level channel on the 

 surface of the lava. The same remarks apply to the volcanic 

 matter at Whangarei and at the Bay of Islands. ThisTvolcanic 

 action, however, appears to have lasted a considerable time. 

 The rocks of the plateau of the lower Waikato are similar to 

 those of the Auckland caves. Though still quite fresh at a 

 little distance from the surface, there is a deep and fertile soil 

 formed from the lava, and streams have cut deep channels 

 through it. The same remarks apply equally to the Bay of 

 Islands. It appears, then, that though the present cones and 

 their lava-flows are of extremely recent age, they represent only 

 the final effort of a long period of activity, which may have com- 

 menced in the Pliocene. 



*Hill, Tram. N.Z. Inst., vcl. xx, p. 301. 

 t Park, Geological Reports, 1886, p. 71. 

 j Hutton, Trans. N.Z. Inst., vol. xix, p. 339. 

 § Hutton, Trans. N.Z. Inst., vol. xxxii, p. 173. 



