PHYSIOGRAPHIC NOTES ON AUCKLAND. 



The beautiful symmetrical Rangitoto fitly stands sentinel in 

 advance of the host of perfect volcanic cones which here, there, 

 and everywhere stud the surface of the gently rolling lowlands of 

 the Auckland District. But the subdued landscape, the numerous 

 tidal creeks, the indented shore-lines, the wave-cut cliffs, all present 

 a history not less interesting than that of the volcanic cones. For 

 the area occupied by Auckland City and northward of it the history 

 is this : A wide belt of weak sediments, flanked westwards by a 

 submeridional volcanic range, has been largely reduced by normal 

 erosion to near sea-level. Elevation of the area ensues, punctuated 

 apparently by two periods of approximate standstill, marked at 

 the present day one most clearly, the other less so by erosion 

 surfaces immediately adjacent to Waitemata Harbour. Both are 

 well below the level of widespread uplands which represent the 

 maturely dissected peneplain of the earlier cycle. Uplift recommences, 

 and deep stream- valleys are excavated in the broad erosion surface 

 now conspicuous at low levels north-westward of Auckland. Suddenly 

 there is a change, and a movement of depression causes the sea to 

 advance into, or " drown," the newly cut valleys, with the result 

 usual in such cases the formation of numerous harbours, inlets, 

 and tidal creeks. 



Since, the " drowning " waves have been actively cutting back 

 headlands, and, with the assistance of tidal currents, insilting the 

 mangrove-dotted inlet-heads, and forming perfect miniature examples 

 of barrier-beaches, spits, and other such shore-line features. The 

 subsidence has now ceased and uplift has again begun, leaving its 

 traces in shore-line platforms, as at Milford, raised about 5 ft. above 

 normal high-water level, and in such small elevated strand-plains 

 as those well displayed near Buckland's Beach. 



Southward from Auckland City, on the other or western coast 

 of the isthmus, lies the extensive Manukau Harbour, and around 

 its shores is an area of totally different character from that farther 

 north. In generalized terms it is a lowland more or less sharply 

 bounded eastward, along a margin due to faulting and flexure, by 

 irregularly warped uplands of resistant rock. It is largely built 

 of soft incoherent silts laid down in a great estuary into which the 

 Waikato River poured its waters, and which was separated from 

 the Tasman Sea by a great barrier-beach, or similar accumulation, 

 extending between resistant headlands nearly thirty miles apart. 

 Behind this beach lofty sand-dunes arose, and, migrating eastward, 

 covered up a portion of the estuarine deposits. To-day the sand- 

 dune range, not yet destroyed by the ever-encroaching waves, forms 

 the western margin of the lowland. 



But the area has meantime been called upon to share the sharp 

 uplift which led to the excavation of the trenches now forming the 

 channels of Waitemata Harbour, and, in like manner to this latter, 

 the present Manukau Harbour had its birth in the movement of 

 subsidence which followed this uplift, and which seems, from evidence 

 in the Manukau area, to have been quantitatively only a few feet 

 less than the latter in its differential effect. 



