470 Transactions. — Geology. 



Bryozoa are common to the greensand and the breccia. 

 Pecten fischeri and Betepora beaniana are common to all three 

 beds. 



The stratigraphical and palseontological evidence are thus 

 both in favour of an Oligocene age. There is evidence also in 

 favour of the supposition that the breccia bad its source in 

 the Waitakerei vents ; and, since those vents are considered 

 Oligocene, such an origin for the breccia strengthens the 

 above arguments. 



My reasons for believing that the source of the Cheltenham 

 breccia was the Waitakerei line of vents are briefly as fol- 

 lows : Firstly, the bed is Oligocene and the vents are Oligo- 

 cene ; undoubted Waitakerei breccias contain a fauna similar 

 to that in the Cheltenham breccia ; and the lava in the range 

 is very similar to the lava in the breccia. Secondly, the 

 Waitakerei vents are the only Oligocene vents not far from 

 the breccia, which can be shown to have had a not distant 

 source ; and the bed grows coarser in this direction, but does 

 not extend to the east. Thirdly, this supposition explains 

 some anomalies in the distribution of the bed. 



I have already given my reasons for considering the 

 breccia Oligocene. With regard to the range I must rely on 

 the observations of others, since I was not able, in the 

 absence of roads and especially in the winter, to explore its 

 forest-clad slopes for myself. The most important observa- 

 tions on the age of the Waitakerei vents are those of Mr. 

 James Park.' ;: 



Mr. Park wrote that his work in 1886 tended to show that 

 the Manukau (= Waitakerei) breccias "originated during sub- 

 marine volcanic outbursts of an intense character, some time 

 during the deposition of the Orakei Bay beds, most probably 

 at the horizon of the Parnell grit and Takapuna [= Chelten- 

 ham] ash-bed. At Komiti Peninsula, and further north, on 

 the Wairoa, marine beds, containing characteristic fossils of 

 the Orakei Bay horizon, are interbedded with heavy deposits 

 of volcanic breccias, tufas, and agglomerates, and occasionally 

 sheets of solid lava, consisting of dolerites rich in olivine, 

 hornblende, and augite-andesites. These can be traced south- 

 ward to the Hoteo and Kaukapakapa, and an examination 

 of the bush country south of the latter will probably show 

 that they are connected with the breccias of the Waitakerei 

 Range. " 



The classing of the Orakei greensand, the Parnell grit, and 

 the Cheltenham breccia as " Orakei Bay beds " is somewhat 

 confusing, and I am ignorant as to what " the characteristic 

 fossils" were to which Mr. Park refers; but, since the out- 



* Trans. N.Z. Inst., 1889. 



