Marshall. — Geology of the Central Eaipara. 437 



on which the Pakaurangi beds rest and the concretionary beds at Batley 

 in which Inoceramus was recorded were classed in the Jurassic. A strong 

 unconformity is indicated in a section showing the stratification of the 

 Pakaurangi Point. This break is represented as occurring between the 

 " chalky marls " (called in the present paper " white mudstones ") and the 

 " Waitemata beds "* or tufaceous beds with fossils. The former of these 

 beds are said to strike north-west and south-east and to dip 60° to the north- 

 east, and the latter strike east and west and dip 20° south. Careful observa- 

 tions failed to support these statements. The white mudstones are traversed 

 by numerous prominent joints which have nearly the bearings stated, and 

 it appears that these have been mistaken for stratification-planes. The 

 true stratification-planes are hard to distinguish, but when found it is seen 

 that they strike 157° and dip 24° north-east. This result was obtained twice 

 in different parts of the exposure at an interval of three years. The first of 

 the observations was made in company with Dr. C. A. Cotton, of Wellington. 



Some 150 yards farther south-east as seen on the foreshore close to 

 Pakaurangi Point the mudstones acquire a bluish tint rather abruptly 

 along a well-defined plane. The strike is here 120°, and 40 yards farther 

 on, where the beds become more sandy and tufaceous (Waitemata beds of 

 Park and Cox), the strike becomes 107°, and again the plane of contact 

 shows no sign of erosion. Though this change of strike within the short 

 distance mentioned may appear considerable and important, other varia- 

 tions as great are found in the Pakaurangi, or tufaceous, beds themselves. 

 The strike here changes from 65° to 110° within a distance of 30 yards, 

 and afterwards to 170°, with accompanying great changes in the dip, as 

 shown in the map of the district. In order to see the stratigraphical facts 

 mentioned the district must be visited at low tide. 



At the extreme end of Pakaurangi Point there is considerable irregularity 

 in the stratification. This is represented by Park as a fault. It might 

 almost as well be represented as a disconformity. The beds here consist 

 of tufaceous material and fine brecciated matter, and at the extreme point 

 contain a large number of fossils of Miogypsina, which is also found below 

 the disconformity. There are also some mollusca, such as Pecten aldingensis 

 Tate, which are also common in the rest of the sandy beds between the 

 sandy white mudstones and the point. The structure at the end of the 

 point is therefore of very little importance. 



McKayf subsequently visited the district and reported a complete con- 

 formity from the Inoceramus beds to the top of the hydraulic limestone. 

 He did not, however, visit the region of Pakaurangi Point. 



The sequence of the younger rocks of New Zealand, so far as it is de- 

 veloped in the Central Kaipara district, appears to give no indication of 

 such a break as is required to mark the dividing-line between two periods of 

 sedimentation- — that is, between two geological systems. Since the hydraulic 

 limestone has always been correlated with the Amuri limestone of North 

 Canterbury, it is natural in this place to review the additional observations 

 that have been made in regard to the stratigraphical relation between this 

 rock and the Weka Pass limestone which rests on it. It must again be 

 stated that this is the dividing plane between Hutton's Cretaceous and 



* J. Park, Kaipara and Wade Districts, Auckland, Rep. Geol. Explor. dur. 1886-87, 

 1887, pp. 219-29 (see esp. p. 221, and section repeated, Geol. Mag., 1911, p. 546). 



t A. McKay, On the Geology of the Northern District of Auckland, Rep. Geol. 

 Explor. dur. 1887-88, 1888, pp. 37-57 (see p. 54). 



