314 The N.Z. Journal of Science and Technology. [Jan. 
be seen at the upper end of the spur referred to above, which separates the 
two branches of the Waiomio Creek. On the south side of the bridge which 
carries the old Onerahi Road over the Awaroa Creek, and on the right bank 
of the creek, the brown sandstones of Mount Tiger which dip beneath the 
crystalline limestone of “ The Abbey,” Whangarei, rest upon the upturned 
edges of claystones belonging to the Onerahi formation. (“ The Abbey,” 
Whangarei, is the spot referred to by Cox* * * § as the “ Whareora Caves.”) 
At Ruarangi Hill, two and a half miles south-west of Whangarei Railway- 
station, crystalline limestone rests upon steeply dipping hydraulic limestone 
without the interposition of the brown sandstone. At Onemama Point, 
Whangarei Harbour, an almost horizontally bedded crystalline limestone 
(at this particular point a calcareous sandstone) covers a brecciated and 
eroded surface of steeply dipping hydraulic limestone. Marked angular 
unconformity is shown at all the above points, as well as in many other 
less accessible localities. The fact that as a rule the Whangarei formation 
rests upon the denuded surface of the Trias-Jura rocks without the inter¬ 
position of the Onerahi formation is evidence of a long intervening period 
of erosion. 
The Ages of the Two Limestones. 
The exact age of the hydraulic limestone is not yet determined, since no 
identifiable fossils have been found in it. McKay has recorded Cretaceous 
fossils from Whangaroa Harbour and in the Waitangi valley opposite 
(west of ?) Waimate North, and also in several localities^ in the Whangarei 
and Bay of Islands Subdivision in deposits of the Onerahi formation. 
Bell and ClarkeJ record fossils of Cretaceous aspect in the lower part of 
their Kaeo series, which would seem to lie beneath the Onerahi beds 
developed in that neighbourhood. Thus the hydraulic limestone cannot 
be older than Cretaceous. Since the Onerahi formation is separated by 
an erosional interval from the Whangarei formation, which contains an 
Oamaruian (Miocene) fauna, the hydraulic limestone cannot be as young 
as Miocene. 
The age of the Whangarei limestone, can be determined with more 
exactitude. In the crystalline limestone Amphistegina, a foraminiferal 
genus, is of common occurrrence. Mr. F. Chapman, of the National Museum, 
Melbourne, states§ that “ whenever it is found abundantly in fossil deposits 
one may conclude we are dealing with Miocene strata.” 
Recent collections of fossils from the Whangarei limestone and associated 
beds have been identified by Mr. J. Marwick, of the Geological Survey staff. 
Fossils from the Takou River, Kawakawa, Hikurangi, Kamo, Awaroa 
Creek, and Te Mata (Hewlett’s) Point prove that the Whangarei formation 
belongs to the Omaruian system, and is therefore of Miocene age. The 
crystalline limestone contains fossils characteristic of the Ototaran stage. 
Conclusion. 
From the above statements it follows that the crystalline (Whangarei) 
limestone is of Miocene age, and belongs to the Ototaran stage of the 
Oamaruian system ; and that the hydraulic (Mahurangi) limestone must 
be late Mesozoic, or possibly early Tertiary. In thus interpreting the strati- 
graphical succession a great advance has been made towards the solution 
of several economic problems. 
* S. M. Cox, loc. cit., p. 102. 
f A. McKay, loc. cit., p. 45. 
j J. M. Bell and E. de C. Clarke, N.Z. Geol. Surv. Bull. No. 8, p. 58, 1909. 
§ Trans. N.Z. Inst., vol. 48, p. 99, 1916. 
