Mulgan. — The Waitemata Series. -117 



Lower Miocene age. These consist of soft or muddy sand- 

 stones and friable shales. An average section usually shows 

 bands of sandstone and softer shales alternating with each 

 other. The sandstones are often hard, and vary considerably 

 in texture from fine to coarse. In a few places they are 

 fossiliferous, though as a rule fossils are absent from the 

 great body of strata, though wood in fragments may occur. 

 The strata themselves vary in thickness from a few inches to 

 several feet, the shales or sandy clays forming, on the whole, 

 much thinner layers than the sandstones, seldom, indeed, 

 reaching a thickness of more than a foot. They are, more- 

 over, much softer than the sandstones, and readily crumble 

 away when exposed to the action either of the weather or the 

 sea. 



A noticeable feature of the series is the horizontal or 

 gently undulating position which, on the whole, the beds 

 maintain. Here and there, however, great disturbances 

 have taken place, resulting in the rupture and dislocation 

 of the strata, the formation of numerous faults, and the 

 consequent obliteration of connecting-links between individual 

 beds. 



To the third group belong Hochstetter's Quaternary beds, 

 consisting of plastic clays and sands, occurring, for instance, 

 along the Tamaki Creek and on the southern shores of the 

 Manukau Harbour. 



The fourth group comprises the Pleistocene lavas and tuffs 

 which have been ejected from the numerous volcanic vents in 

 the neighbourhood and spread over the greater portion of the 

 isthmus. The lava, consisting entirely of basalt, varies much 

 in texture. It is, on the whole, a hard compact rock, and is 

 always rich in olivine. (See rock section E, Plate XXVI.) 



Section IV. — Grit-beds on South Side of the Auckland 



Harbour. 

 On the eastern side of Judge's Bay there occurs a band of 

 volcanic grit some 10 ft. in thickness dipping west at an angle 

 of about 12°. The band consists of fine volcanic material, the 

 fragments ranging from minute specks to particles somewhat 

 larger than a pea. The whole is firmly united together, and 

 forms a reef which runs about 100 yards into the harbour and 

 is exposed at low water, its hard character enabling it to 

 withstand the action of the waves, which have worn away 

 the softer sandstones and shales. It lies conformably be- 

 tween other members of the Waitemata series, is distinctly 

 marked off from the layers both above and below, and 

 can be traced round Point Resolution, where it forms a 

 long outcrop on the western side of Hobson's Bay. About 

 three miles further east, at St. Helier's Point, and again at 

 27 



