454 Transactions. — Geology. 



southerly direction, keeping well to the east of the peninsula,, 

 and receiving on its way the Whakapara and Mangahahuru 

 Streams, both of which come from the east, and drain the 

 country almost to the seaboard. 



The Mangakahia rises on the southern slopes of the water- 

 shed separating the Hokianga and Kaipara basins, and, gather- 

 ing supplies from the northern and eastern slopes of Tutamoe, 

 skirts the Tangowahine range, receives further down the 

 Hikurangi from the north, and finally unites with the Wairtia 

 at the Junction. 



The Kaihu, which drains the basin to the west, is worthy 

 of note in that it receives supplies from streams some of 

 which rise not far from the source of the Mangakahia, and 

 others almost at the coast. The Kaihu itself , moreover, keeps 

 parallel to the coast until it reaches the Wairoa at Manga- 

 whare. 



The Mangonui rises on the western slopes of the hills to 

 the west of Waipu, and, flowing north-west, is joined by another 

 large stream, the Tauraroa. From here its course is first 

 west and then north until the Wairoa is reached. 



It will be seen from this that the catchment-area prac- 

 tically includes the whole of the land from coast to coast, 

 and stretches from a line joining the mouth of the Ho- 

 kianga Harbour and the upper waters of the Bay of Islands 

 as far south as the Kaipara Harbour. That is to say, bear- 

 ing in mind the configuration of the country, the river-basin 

 comprises the maximum area available. These singular con- 

 ditions have been made possible by the distribution of the 

 high land. It usually happens that the highest land of a 

 country occurs in the centre, and the lower levels are found 

 near the coast. In the case of the Wairoa basin these con- 

 ditions, although not entirely reversed, yet are considerably 

 modified. The greater part of the land is high ; indeed, 

 nearly the whole of the central portion of the basin con- 

 sists of broken, bush-clad ranges, some of which reach an 

 elevation of from 1,500 ft. to 2,000 ft. (Tutamoe, the highest. 

 peak north of Auckland, has an elevation of 2,576 ft.). These 

 ranges, whose general trend is from north to south, are cut 

 across in many places by narrow valleys, and Hanked on 

 either side by low hills running parallel to the seaboard. 

 Thus, the whole of the rainfall on this portion of the pen- 

 insula, instead of being carried to the sea by a number of 

 different streams, is collected to furnish the supply for a single 

 river. 



The size and configuration of the catchment-area would 

 not in themselves accovmt for the volume of water discharged 

 by the river. A more important factor than either is the rain- 

 fall, which in this particular case must reach phenomenal 



