180 Transactions. — Geology. 



Changes in Physical Geogeaphy. 



New Zealand also offers for solution many problems in 

 physical geography, due to the changes which have taken 

 place since the Cretaceous period, which are very interesting 

 to those who know the ground. But time warns me that I 

 can only glance at a few of them. 



Lake Wakatipu and the Arrow Eiver formerly drained inta 

 the Oreti Eiver by Kingston and the Dome Pass. Subse- 

 quently, the Kawarau and Dunstan Gorges were cut, which 

 allowed the lake to flow into the Clutha. This change seems 

 to have been due to the moraine at Kingston blocking the 

 former channel, and causing a lateral overflow at the Arrow 

 Bluff. To the same cause — i.e., to morainic deposits — we 

 must attribute the change in the drainage of Lake Heron 

 from the Eangitata into the Eakaia Eiver. The Shag Eiver 

 at one time drained the Maniototo Plains, until the gorge 

 of the Upper Taieri was cut. In early Cretaceous times the 

 Hurunui and the Waiau-ua united, and entered the sea at 

 Kaikoura. At a later time they turned down the Weka Pass, 

 and it was not until the Pliocene period that each cut its own 

 valley to the sea. The Upper Manawatu flowed into the 

 Wairarapa, and in the older Pliocene a river ran from near 

 the Manawatu Gorge to Napier. The courses of all these 

 rivers were changed by the deposition of marine rocks in the 

 valleys, which blocked them ; and this, on the subsequent 

 rise of the land, caused the rivers to overflow to one or the 

 other side, according to the position of the lowest opening. 



The Eiver Waikato at first flowed through the Waiotapu 

 Valley into the Bay of Plenty. Its direction was disturbed 

 by volcanic action in the Eotorua district, and its course was 

 then deflected into the Hauraki Gulf. There it remained 

 until the gorge at Taupiri was cut. What caused this last 

 movement has not yet been clearly made out ; but probably 

 it was due to changes in level during the last upheaval of 

 the land when the dome was formed on which Tongariro 

 and Euapehu now stand. '•' 



Summary. 



I will conclude with a short summary of the results at 

 which we have arrived. 



Of what took place on this part of the earth's surface 

 during the early Palaeozoic era we know next to nothing; 

 but towards the close of the Devonian period land certainly 

 existed, although its outlines are quite uncertain. This land 

 must have sunk, for in the Carboniferous period a deep sea 

 rolled where New Zealand now is, while far away to the 



* Cussen, Trans. N.Z. Inst., vol. xxvi., p. 398. 



