264 G. A. Cotton — BJ-^li Mountains in New Zealand. 



Fold Scarps. — Simple fold surfaces and fold surfaces broken 

 by a succession of small faults will give rise to forms very 

 similar to those just described except in their earliest stages. 

 Eemoval of a weak cover from a fold surface will be rapid and 

 result in the exposure of some portions of the sloping floor 

 beneath; but the graded profile of the streams may be so steep 

 that deep cutting is not favored. Further increase in the 

 depth of ravines will then take place only as a sequel to head- 



FiG. 9. 



Fig. 9. Maturely dissected scarp of the Kakanui-Horse Range descending 

 southwestward to the Shag Valley fault angle in north Otago. The stripped 

 plateau descending in the opposite direction to meet the fault scarp is seen 

 in the foreground, and, to the right of the center of the foreground, the 

 gorge of the Shag River superposed on the undermass. 



ward erosion, which may be so slow that flat areas will persist 

 for a comparatively long period, though they may be steep 

 compared with the stripped plateaus of the back slopes. With 

 steeper initial fold surfaces, consequent graded streams may be 

 so deeply incised as to maturely dissect the surface of the 

 oldermass, except, perhaps, for a few facet-shaped remnants. 

 The resulting form is indistinguishable from a maturely dis- 

 sected fault scarp. Vigorous streams may be expected to push 

 back the crest line divide, which will recede in the stage of 

 maturity down the back slope of the block. A good example 

 of a submaturely dissected fold scarp is the eastern face of the 

 northern end of the Blackstone Hill block (see fig. 10). Of 

 the same nature are the side slopes of a broad saddle of cate- 

 nary form separating the stripped plateau of the Gouland 

 Downs from the depression of the lower Aorere Yalley in 

 northern Nelson (Cotton, 1916 V) and probably many other 

 scarps in the same region. 



