118 Transactions. 



unimportant shore progradation, or where at Port Fitzroy the cliffs are 

 interrupted temporarily by deep, narrow entrances to the wonderful and 

 beautiful harbour. 



Delta - building is active in bay - heads entered by streams of any 

 importance, but there is a noteworthy absence, even in the landlocked 

 Fitzroy Harbour, of the mangrove-dotted mud-flats so common in most 

 of the North Auckland harbours. This is to be accounted for in part 

 because of the insignificant size of the inflowing streams, in part because 

 of the great depth of the sea-occupied trenches. 



The eastern coast of the island differs very greatly from the western. 

 It is exposed to more vigorous wave-attack from the ocean, with the result 

 that it has been cut back until the coast-line is much more regular than 

 the western. Several large harbours similar to Port Fitzroy existed at 

 one time, but all have been shut off from the open sea by spits or barrier 

 beaches, and the resulting lagoons have in large part been obliterated by 

 blown sand and swamp or other filling. One of the best examples is 

 furnished by the lower Kaitoke area, in the central portion of the island 

 The earlier inlet has apparently been enclosed by a barrier beach. Land- 

 wards from this is a zone of low sand-dunes, and then comes a remarkable 

 area of swamps. (See Plate XXII, fig. 2.) At the Awana Stream, similarly, 

 swamps occupy an extensive tract within a flaring portion of the lower 

 valley, just above a bottle-necked outlet to the ocean which is due to the 

 close approach of two opposed spurs cut in resistant andesitic fragmentals. 



Barrier Beaches or Spits. 



In considering whether the former harbours of the eastern coast of 

 Great Barrier Island have been blocked off by barrier beaches or spits 

 one has many opposing considerations to weigh. The problem is best 

 considered by reference to the analogous physiographic conditions of the 

 Cape Colville Peninsula, where, in similar manner, the western harbours 

 remain open, whilst the eastern are largely shut off by wave-built sand- 

 accumulations. 



There is undoubtedly a strong northward drift of the sea-waters, which 

 brings pumice, for example, from the Bay of Plenty around Cape Colville 

 and deposits it in such places as Whangateau (near Cape Rodney) on the 

 shores of the mainland ; but this cannot have had any effect in creating 

 the present conditions at Great Barrier Island, for both coasts should show 

 similar features if this were so. 



The fundamental reason undoubtedly is that which has allowed the 

 building of such typical barrier beaches as the somewhat complex one that 

 encloses the Katikati-Tauranga harbour, on the southward continuation 

 of the east coast of Coromandel Peninsula. There is abundant evidence 

 that the waves of the open ocean have in that district removed a very 

 considerable strip of land in cutting back the present sea-cliffs. 



It is also to be observed that the depth of water off shore at the con- 

 clusion of the major movement of subsidence noted was shallow wherever 

 barrier beaches have been built, for in such localities the earlier land- 

 surface was invariably of low relief, often consisting of the flood-plains 

 of the now greatly diminished rivers, or of the flatfish floors of their wide, 

 late-mature valleys. The initiation of the building of the beaches is 

 almost certainly to be correlated with sub-recent uplift of a few feet, which 

 is demonstrated by uplifted shore-terraces, wave-cut platforms, sea-caves. 



