Cotton. — Rough Bulge and its Splintered Faidt-scari:). 



283 



Rough Ridge. 



The back slope of Rough Ridge is probably the most perfectly preserved 

 inclined fossil plain in Otago. The surface, as shown in fig. 3 of the paper 

 referred to above, is in the stage of erosion when the overmass has been 

 stripped off and the ancient planed floor is undergoing dissection by nume- 

 rous parallel consequent streams none of which is master. While a few 

 feet of rock have been removed from the stripped floor since the removal 

 of the cover, as is shown by the presence of abundant residual tors of 

 schist, the form of the ancient eroded plain, now tilted with an inclination 



Fig. 2. — Diagram of a splintered fault 

 dislocating a plane surface. 



Fig. 1. — Northern end of Rough Ridge (from 

 maps by Department of Lands). 



of 10^, is preserved almost perfectly by the existing surface of the inter- 

 fluves. Though these are narrow, they slope towards the numerous stream- 

 lines only near their edges, which are rounded off. The profiles of the 

 little valleys of the dissecting streams are roughly graded, though incised 

 to but a small depth below the general slope, this depth being, as would 

 be expected, greatest about the middle of the slope. Thus, if the former 

 presence of a cover be disregarded, the cycle of erosion for the surface is 

 still in the stage of youth ; and it may remain, and probably has remained, 

 at this stage for a long period, for the conditions are here extremely 

 favourable for long persistence of such pseudo-youthful topography.* In 

 this way only can the frequent recurrence of similar back slopes be 

 explained . 



* C. A. Cotton, loc. cit., p. 259. 



