Maxwell. — On Changes in the Coast-line. 565 



marked on the west coast. They consist of apparent encroach- 

 ments of the sea on the land, and a gradual eating-away of 

 those portions of the coast-line which, not being protected by 

 dykes of hard rocks or banks of drifted sand, are exposed to 

 the wash of the tides. In many places that I can call to mind 

 between the Manukau Heads and the North Cape this process 

 of denudation is going on at an active rate. 



In the Manukau Harbour extensive stretches of mud-flats 

 exist, with stumps of trees, some of them of great size, still 

 showing, though in most cases they have been eaten level with 

 the surface by the Teredo navalis. 



In the Whangape Harbour in particular, within the memory 

 of men still resident there, many acres of once-cultivated land 

 have been swept away, and nothing is now left but bare mud- 

 flats, showing here and there the stumps of some of the larger 

 manuka or other woods sufficiently deeply embedded in the 

 subsoil to resist the ravages of the waves for a time at least. 

 So persistent is the attack of the sea that the Natives have 

 been compelled to protect the face exposed to the waves with 

 breastworks of split timber, in order to save some of their most 

 fertile kumara plantations from totally disappearing. 



These facts seem to indicate that at some previous period 

 most of these mud-flats were low-lying stretches of alluvial 

 land, covered with forest, which have been encroached upon 

 by the wash of tides gradually rising higher, and the vegeta- 

 tion destroyed by the salt water, until finally nothing was left 

 but the present stretches of mud-flat, bare for miles at low 

 water. 



The coast-line from Kaipara Heads to Maunganui Bluff, 

 many miles in length, shows very distmctly that the sea has 

 made inroads on the solid land, or, in other words, the land 

 projected much further into the ocean at one time than it does 

 at present. 



The coast-line is remarkably straight, and, as the formation 

 is similar throughout, the erosive action must be very regular 

 along the whole line. 



The general appearance of the coast is a very flat, hard 

 beach, with very little shifting sand, extending to the base of 

 soft sandstone cliffs ranging from 60ft. to 100ft. in height. 

 During high spring tides, with westerly winds or westerly galeS^ 

 generally, the seas beat against the foot of the cliffs and wash 

 out the softer seams of sandstone, when, the face being under- 

 mined, large masses break off and come tumbling down on the 

 beach to be speedily swept away by the breakers. 



Exposed in the face of the cliffs are seams of lignite, one 

 above the other, ranging from a few inches to several feet in 

 thickness. This substance appears to be of recent origin, for 

 in places huge trunks of trees belonging to the natural order 



