43(5 Transactions. — Geology. 



the Mahia and the intervening area was covered with blue-elay 

 sands and marls, or with limestones. It was at this period that 

 great changes began towards the interior of the Island. The 

 volcanic district was the centre of unusual disturbances, and the 

 country between it and us was broken, and swept by floods of 

 shingle and sand, alternating with showers of pumice, that spread 

 over the country to the northward of parallel 39 - 40° S. At that 

 time the watershed of the Taupo country was directed towards 

 the north-east, and it was from the country in the vicinity of the 

 present Mohaka River source that the heavy deposits of shingle 

 and sand appear to have come. The shingle and pumice deposits 

 extend from Pohui, at the base of Te Waka, on the Taupo Road, 

 south-west along the Matapiro country into the Ruataniwha 

 Plain, and thence generally southward, replacing the limestones 

 that flanked and that also covered at one period what are now 

 the Ruahine Mountains. Similar deposits fanned to the eastward, 

 and spread as far as the Black Reef at the Kidnappers, the shingle 

 and sand deposits between Pohui and Petane, along the present 

 Napier-Taupo main road, being very largely developed. It was 

 following the comparatively rapid deposition of shingle, sands, 

 and pumice that the period of subsidence began which ended 

 in the complete disappearance of the immense area extending 

 from the Mahia Peninsula right away to the hills between the 

 present Pakipaki and Maraekakaho. whilst the rifts or fractures 

 that were made extended from Pakipaki to the Te Aute Lake, 

 and from Maraekakaho on and on in an irregular line into the 

 Ruataniwha district, where subsidence took place in a large 

 measure corresponding and parallel with the line of elevation now 

 known as the Ruahine and Kaweka Mountains. As remarked 

 already, during the subsidence areas like Scinde Island. Fernhill. 

 Roy's Hill, the Watchman, and a number of others of less 

 importance became islands, separated from the mainland and 

 washed by the incoming ocean. 



The subsidence of such an extent of land as covered Hawke's 

 Bay and what is now the Heretaunga Plain, in combination with 

 the volcanic disturbances that continued in the centre of the 

 Island, brought changes in the surface-features of the country 

 that have resulted in what is now recognised as the river system 

 of Hawke's Bay. The Tukituki River, even after the disap- 

 pearance of the river which I may call the Greal Wairarapa, 

 of which it formed a tributary, continued to flow southward. 

 but the throwing-out of heavy fanlike deposits from the rising 

 Ruahines, by menus of the mountain-streams flowing eastward, 

 eventually dammed back the main river at the south end beyond 

 Takapau. and thus formed the Ruataniwha into a large lake. 

 The rilling of this lake, and its eventual overflow at what are now 



