Cotton. — Notes on Wellington Physiography. 251 



Divides in the Tongue Point cycle have in some cases been reduced to 

 a fairly low altitude. Where they stand only 600 ft. to 800 ft. above 

 present sea-level they have been rounded and their slopes graded, and 

 rock outcrops are few. Higher-standing ridges are more rugged, with 

 rock outcrops and sharpened summits, except where they are flat-topped,, 

 and forms of the Kaukau cycle remain. 



The broad upland features in fig. 3 belong to the Tongue Point cycle. 

 The Ohariu and other streams, however, shown in the figure have been 

 revived, and reaches have been graded and widened with the formation 

 of flood-plains. These belong to the present cycle. 



The Present Cycle. 



Forms of the present cycle comprise the steep lower slopes of valley- 

 sides and the flood-plains developed along portions of the courses of the 

 larger streams. The Makara-Ohariu system may still be retained as an 

 example (figs. 3 and 4). The streams are not yet graded throughout their 

 length, but a number of flat-floored graded reaches have been worked out, 

 the flood-plains of which "are extensive enough to be cultivated. These 

 reaches are invariably strictly parallel to the strike of the rocks. The 

 long graded reach of the east branch of the Ohariu shown in fig. 3, for 

 example, is incised only to a depth of about 50 ft. below the flood-plain 

 of the earlier cycle. Where it turns sharply to the south-west its bed 

 is 250 ft. above the sea. It then follows an entrenched meandering 

 course in a young gorge diagonally across the strike, and falls 240 ft. 

 in two miles. 



The present cycle, therefore, cannot be said to have passed its early 

 youth. 



The Port Nicholson Area. 



East of the ridge upon which Kaukau Peak stands there is a 

 complicated topography, the result of subsidence of the Port Nicholson 

 block. The writer is inclined to believe that either the original bound- 

 aries of the subsided block were broad flexures rather than faults, or, 

 on the other hand, the original subsidence took place so long ago that 

 topographical evidence of faulting has been obscured by subsequent 

 denudation. The numerous fault-lines suggested by Bell* run parallel 

 with the strike, and for this reason old faulting along these lines would 

 not be rendered recognizable by revival of erosion. 



The north-western portion of Port Nicholson was, however, un 

 doubtedly let down by faulting at a relatively recent date, for along the 

 north-western shore of the harbour there is a clearly defined fault-scarp 

 (see fig. 9). Faulting along this line (the Wellington fault, see p. 257) 

 took place perhaps along with, but more probably after, the submergence 

 of the main portion of the Port Nicholson block. The fault and, in 

 general, the subsidence of the whole block have provided the drainage 

 of the whole area with a much shorter and therefore steeper descent than 

 it formerly had. Two of the active torrents which descended the steep 

 slope quickly succeeded in cutting back so as to tap the drainage of a 

 broad mature valley, the floor of which stood 500 ft. and more above 

 present sea-level (see " Changes in the Drainage of the Karori-Khandallah 

 Valley," p. 262). 



* Trans. N.Z. Inst., vol. 42, 1910, map and section, pp. 537, 539. 



