14 W. N. BENSON 



composed usually of hard graywacke or schist, on the more or 

 less planed surface of which rested much less resistant Tertiary and 

 sometimes Cretaceous sediments. In many elevated blocks 

 the hard basement rocks rose to a higher level than the compara- 

 tively weak covering strata in the adjacent relatively depressed 

 blocks, which formed broad, fault-bounded, intermontane basins 

 or narrow, rectilinear rift valleys, or fault-angle valleys. A conse- 

 quent drainage was soon established on the broken sheet of covering 

 rocks, which it commenced to remove. Where this process is 

 still incomplete, topography is controlled in large measure by the 

 variation in the resistance to erosion offered by the different strata 



YAR05 



Fig. 4. — Section at Lake Wakatipu showing extensive movement in the post- 

 Tertiary orogeny, a, sandstone and conglomerate; b, limestone; c, marly sandstone; 

 d, marly clays; e, brecciated Tertiary marine rocks; m.s., mica schist. (After Park.) 



in the covering rocks, and dip slopes and scarps are characteristic 

 features of the scenery. Where, however, erosion is more advanced, 

 portions of the planed surface of the underlying rocks are laid bare, 

 and where the cover is cleared away from extensive areas, a stripped 

 peneplain is exposed, the further reduction of which is very slow 



(Fig. 5)- 



Late erosion. — An enormous amount of detritus results in the 

 stripping of the covering strata from the surface of the elevated 

 blocks and from the dissection of the fault-scarps. This is only 

 exceptionally removed as it is supplied. In most places deep 

 aggradation of the troughs has taken place concurrently with the 

 dissection and degradation of the higher blocks. 



