360 Transactions. — Geology. 



great difference between the mean density of the materials 

 forming the accessible portion of the crust of the earth and 

 the mean density of the globe as a celestial body. The oldest 

 sedimentary rocks in New Zealand are certain flagstones, 

 slates, and quartzites forming the core of the Pikikiruna 

 Eange, lying between the Motueka and Takaka Valleys, in 

 Nelson. These underlie a vast development of Lower Silu- 

 rian rocks, and in my report on " The Geology of the County 

 of Collingwood" (Geological Eeports, 1888-89) I classified 

 them as Cambrian. They do not appear to have been in- 

 truded by contemporaneous igneous outbursts, and therefore 

 supply no information relating to the present inquiry. 



In the Silurian period were erupted acidic lavas, forming 

 granites and syenites ; in the Devonian period, basic lavas, 

 forming diabases, basalts, and ultrabasic serpentines and 

 peridots ; and in the Carboniferous period, acidic lavas, form- 

 ing syenites. From the Permian period, through the whole of 

 the Secondary formations up to Eocene times, there appears 

 to have been a general cessation of volcanic activity in the 

 New Zealand area. After this long period of quiescence, 

 volcanic energy of a most violent, devastating, and wide- 

 spread nature manifested itself towards the close of the 

 Eocene formation. There is abundant evidence to show that 

 this sudden display of pent-up energy was accompanied by 

 severe and prolonged earthquakes, causing the formation of 

 deep fissures and great faults. The faults which originated at 

 this time were numerous and deep-seated, and caused many 

 permanent modifications in the physical features of the coun- 

 try. At the Port Hills, Nelson ; at Shakspeare Bay, Picton ; 

 along the whole course of the Inland Kaikoura Mountains ; at 

 Lake Wakatipu ; at Martin's Bay and Big Bay, on the west 

 coast of Otago ; and at many other places in New Zealand, 

 hundreds of feet of strata have been involved among old 

 Palaeozoic rocks by great faults, some of which have esta- 

 blished themselves along lines of weakness along which dis- 

 placements have taken place at intervals up to the present 

 time. It was probably at this period of eruption that the 

 great continental area which was supposed by Hochstetter to 

 have existed off the west coast, and of whose existence proofs 

 are not wanting, became finally submerged in the Pacific 

 Ocean. At this later Eocene period were doubtless erupted 

 the great series of auriferous pyroclastic tuffs and andesites 

 of the Hauraki Goldfields, and also the basic and semi- 

 basic lavas and tuffs at Banks Peninsula, Oamaru, and Port 

 Chalmers. 



The next grand outburst of volcanic activity took place in 

 Pliocene times, and converted the central portion of this 

 Island into one vast theatre of volcanoes, discharging showers 



