260 C. A. Cotton — Block, Mountains in New Zealand. 



the highest portion of a block to a neighboring trough takes 

 place by a fault or flexure followed bv a sloping surface (see 

 fig. 6). Streams of large volume from the higher block will 

 destroy the lower, gently sloping surface with its deep ravines. 

 Such is the dissection of the northwestwardly sloping surface 

 which descends to the Aorere fault-angle depression in north- 

 west Nelson (Cotton, 1916, pp. 66-68). 



Fig. 5. 



Fig. 5, Dissection of the steeply inclined back slope of a faulted block 

 by consequent and insequent ravines. The initial form is shown on the 

 risht. 



Fault Scarps and Fold Scarps. — Except for the possible 

 case of antecedent drainage crossing an uplifted block in a 

 direction opposite to that of the general slope of the tilted sur- 

 face and emerging from gorges on the steeper side of the block, 

 the dissection of the steeper sides of asymmetrical blocks with 

 the structure postulated will be effected entirely by consequent 

 streams. AYhen they have steep fronts the blocks are bounded 



