1922 .] 
Departmental Report. 
313 
the hydraulic limestone, and it agrees with Hutton’s view as to the position 
of the North Auckland coal. This point is of prime importance, since on 
it depends the distribution of possible coal-bearing areas. That the coal 
is Oamaruian in age is now beyond doubt, for marine Oamaruian fossils 
have been found in closely associated beds both above and below, and the 
Whangarei limestone with Amphistegina and other Tertiary forms occurs 
not far above the coal. Up to the present no indications of coal have been 
seen in or beneath the Onerahi formation, and coal would seem to be absent 
in those areas where the Whangarei strata rest upon the denuded surface 
of the rocks of the Onerahi formation. 
The Interpretation of the Geological Column. 
The observations and deductions made by other workers in this district 
may be found in the older reports of the Geological Survey and in recent 
volumes of the Transactions of the New Zealand Institute , where also lists of 
papers dealing with this subject are given.* * * § In the following paragraph 
the divergent views there promulgated are comjiared with the results 
obtained by a systematic mapping of a particular area. 
Hectorf thought the coal-measures of North Auckland to be at the 
base of his Cretaceo-Tertiary formation, and made them dip beneath the 
hydraulic-limestone series as they seem to do at Kawakawa. The Whangarei 
limestone had to accompany the coal. McKay{ similarly always main¬ 
tained that the Whangarei limestone was below the hydraulic limestone. 
A careful perusal of his reports gives the impression, however, that after 
he had found fossils of Tertiary facies at Kawakawa he was not really sure 
in his own mind on this point. He also correlated the hydraulic limestone 
with the Amuri limestone. Hutton§ was aware that Oamaruian fossils 
had been found in beds below the Whangarei limestone, which was sup¬ 
posed to underlie the hydraulic limestone, and showed that, if this was 
the case, the hydraulic limestone could not be correlated with the Amuri 
limestone. 
McKay’s|| section at Waiomio has been quoted in recent discussion. He, 
however, seems to have misinterpreted the evidence here, for, although the 
hill which his section shows to be composed of hydraulic limestone does 
belong to that formation, the Whangarei limestone, which is shown as 
passing beneath the hydraulic limestone, does not do so ; it has been found 
to rest upon it on the same spur of which the hill forms part. 
Cox has shown the stratigraphical succession at Limestone Island and at 
Mount Tiger by two clear diagrams.In the first the impression is given 
that an unconformity exists between the Whangarei limestone and the 
hydraulic limestone ; in the second he shows a confoimable series from 
the top of the Whangarei or crystalline limestone to the brown sandstone 
resting upon the slate rocks. He always writes of an upper (the crystalline) 
and a lower (the hydraulic) limestone, and remarks that in certain cases 
coal appears below the upper limestone and brown sandstone. 
The present survey has shown that the Whangarei limestone is younger 
than the hydraulic limestone, and the weight of evidence that has accumu¬ 
lated is now sufficiently great to put an end to the long controversy which 
has centred about the relative ages of the two limestones. Stratigraphical 
superposition of the crystalline limestone upon the Onerahi formation may 
* J. A. Thomson, Trans. N.Z. Inst., vol. 52, p. 420, 1920. 
f J. Hector, Rep. Geol. Explor. dur. 1892-93 (No. 22), p. xii, 1894. 
j A. McKay, Rep. Geol. Explor. dur. 1887-88 (No. 19), p. 55, 1888. 
§ F. W. Hutton, Trans. N.Z. Inst., vol. 22, p. 380, 1890. 
!| A. McKay, loc. cit., p. 43. 
Tf S, H. Cox, Rep. Geol. Explor. dur. 1876-77 (No. 10), p. 96, 1877. 
