432 Transactions. — Geology. 



ate, as though the volcanic explosions of former times burst 

 through and ruptured the sedimentary strata, fragments of 

 which were eventually enclosed with the conglomerate. 



The lava-streams of this district are, on the whole, very 

 much alike. They consist of a hard compact rock slightly vesi- 

 cular, showing abundant augite and feldspar crystals. The 

 augite is plentiful, but none of it is very large. I have ex- 

 amined a considerable number of rock sections from these 

 lava-flows, and have found the rocks similar — indeed, almost 

 identical — with those already described from the fragments 

 in the volcanic grits. They differ from these only in the 

 absence of olivine ; but, as this mineral is not an essential 

 constituent, its presence or absence is a matter of but small 

 importance. 



Section VIII. — Summary and Conclusion. 



It will be seen from the foregoing that these volcanic grits 

 are spread over a considerable area on both sides of the Auck- 

 land isthmus, and that they invariably lie conformably be- 

 tween the sandstones and shales comprising the Waitemata 

 series. It is clear, moreover, that the material, although 

 arranged by water, has not been brought from any great dis- 

 tance ; at least, the larger fragments could not have been car- 

 ried far. A careful comparison of the sections described — and 

 these, it must be remembered, were taken from exposures 

 separated by considerable distances — shows that the rocks 

 differ only in the presence or absence of olivine, and that this 

 difference is one not between separate exposures on the same 

 side of the isthmus, but between those on opposite sides. 

 Moreover, this difference is so slight that it hardly deserves to 

 be considered at all, the rocks being identical in all essential 

 mineral contents and in specific gravity. 



Stratigraphically there is no evidence to show that all the 

 outcrops belong to one and the same band ; but the close cor- 

 respondence between the fragments of rock included in them, 

 their similarity in texture, in bedding, in arrangement, and in 

 fossil contents, and, further, the fact that in no case, except 

 at Shag Point, is there any exposure showing more than one 

 band, whereas in several cases a connection can be traced 

 between separate outcrops, all furnish evidence which points 

 towards the probability of the various exposures being con- 

 nected together. There seems little doubt that this is the 

 case with the exposures on the southern side of the Auckland 

 Harbour. Between the ash-beds at Cheltenham Beach, 

 Takapuna, and Eed Bluff the connection has not been esta- 

 blished ; but the great similarity presented by these ex- 

 posures, and the fact that the several outcrops showing at 

 Cheltenham Beach can be correlated, as can also those ap 



