MuLGAN. — Tiic Northern Wairoa. 453 



EXPLANATION OP PLATES XXXV. AND XXXVI. 



Plate XXXV. — Section prom Waitaki River to Mount Mary. 



Reference. 



[a.) Claystones and sandstones. 



[b.) Sandstone conglomerate. 



(c.) Phyllites. 



(d.) Banded phyllite and quartzite. 



(e.) Altered sandstones, &c. 



(/.) Sandstones, gritstones, &c. 



(g.) Slates and flaggy sandstones. 



(i.) Grey sandstones, and flaggy claystones. 



Plate XXXVL — Plan of Part of Waitaki Valley, showing Posi- 

 tion OF Mount Mary. 



Abt. XXXV. — The Northern Wairoa. 



By E. K. MuLGAN, M.A. 

 \_Read before the Auckland Institute, 21st September, 1903.] 

 The Northern Wairoa is in several respects a wonderful river. 

 Eising in a narrow peninsula, it is wliolly confined to a rela- 

 tively small extent of country. The entire catchment-area, 

 indeed, does not measure more than fifty miles by forty 

 miles, and yet this gathering-ground is able to furnish suffi- 

 cient water to supply a river which is navigable for the largest 

 ships for upwards of fifty miles, and for smaller craft for 

 nearly double that distance. Can any other river in New 

 Zealand show a similar record ? Throughout the lower part 

 of its course the fall is so slight that the influence of the 

 tide is felt beyond the " Junction " (i.e., junction of Mangakahia 

 and Wairua Elvers), a distance of more than a hundred miles 

 from the Kaipara Heads. 



The term " Northern Wairoa " is used in the title of this 

 paper in a somewhat wider sense thaii that in which it is 

 generally employed, this name properly belonging to that 

 portion of the river between the Kaipara Heads and the 

 " Junction." 



The streams forming its head-waters are known as the 

 Mangakahia and Wairua (the latter in its upper reaches re- 

 ceiving the name of the Waiotu), both of which drain the 

 northern slopes of the basin, the former to the west and 

 the latter to the east. The two streams gradually converge, 

 and finally meet at what is known as the "Junction." Other 

 tributaries are the Kaihu and Tangowahine, flowing south, and 

 the Mangonui, draining the basin to the south-east. 



The stream known in its lower course as the Wairua rises 

 a few miles to the east of Kawakawa, and not far from the 

 upper waters of the Bay of Islands. From here it flows in a 



