512 NKW ZEALAND SOUND (AND LAKE) BASINS, 



They suddenly precipitate themselves (Plates xl. and xli.) over 

 enormous ledges into knife-shaped clefts. Generally, after 

 traversing these torrent-tracks for several miles only they have 

 established themselves thus early some 2,000 to 2,500 (Plate xl.) 

 feet below the mature valley level, while 30 or 40 miles down, but 

 still 150 miles from the sea, their channel bases rarely exceed 

 heights of from 500 to 600 feet above base-level. In every case 

 where traversing hard rocks they occupy V-shaped canons, show- 

 ing the absolute impotency of lateral corrasion at these points; 

 in other words, the transitional grade has not yet been attained. 



The Clarence River (New England). — -This is a stronger stream 

 than the Macleay, but of identical age, and has cut its channel 

 still more closely to base-level. Along the south arm, and nearly 

 200 miles from the sea, the height above base-level is about 400 

 feet. Here enormous basins occur in the channel, showing the 

 effects of floods. Yet in the hard rocks it flows as a profound 

 defile, showing that even its weak grade has not nearly reached 

 the transitional stage. 



In all these examples incipient plains are being formed near 

 the river mouths, but here for nearly 100 miles inland the grades 

 of the streams are practically nil. Before plain-making can pro- 

 ceed in the hard central areas, the channel grades must be still 

 considerably reduced; that is, at that stage they will be but 

 slightly above sea-level. 



iii. Western Slope of New England. 



The Namoi near Manilla and the Gwydir at Bingara exhibit 

 similar features to those of the eastern streams. The Gwydir 

 here issues from a remarkable gorge cut in a hard Palaeozoic 

 plateau (Upland Valley) from 2,200 to 2,400 feet high. It is 

 1,700 miles from the sea, but only 1,000 feet above that level. 

 The immense " Black-soil Plains," however, distant some 70 to 80 

 miles by stream and 700 feet above sea-level, form a local base- 

 level. 



From a comparison thus of the New Zealand fiords (and canons) 

 with the flood channels of northern New South Wales rivers, and 



