PRESIDEJSrr S ADDRESS^SECTION C. 



Ill 



a ba&emieiit of hard greywaeke or schist, upon the more or less 

 planed surface of which rested less resistant Notccene sediments, 

 which had not infrequently subsided among the older rocks, either 

 in broad " intermontane basins ", enclosed between roughly paral- 

 lel faults, or between a warp and a fault (a " fault-angle depres- 

 sion"), or in narrow rectilinear rift-valleys, sometimes crossed 

 obliquely by other fault-lines or faulted strips, and sometimes re- 

 duced to a narrow wedge-shaped mass of sediment dragged down 

 along a single fault line or even to a mere- zo^ne of fault-breccia ^ 

 such zones sometimes forming a more or less reticulated arrange- 

 ment . 



(III.) The effects resulting frcm the denudation of such a di- 

 versified area have been studied in detail by Cotton, Henderson 

 and Speight. A consequent drainage must ultimately have be- 

 come established, and commenced to remove the covering strata 

 from the tilted or elevated blocks. Where this process is still in- 

 complete, the topography is contrclled in a large measure by the 

 variation of the resistance offered to erosion by the different beds of 

 the covering strata, a,nd dip-slo'pes and scarps are characteristic 

 features of the scenery. Such cuesta-country is especially well-deve- 

 loped in the eastern slopes oif the Ruahine Range, leading down to 

 Hawkes Bay, but it is widespread throughout the Hawkes Bay 

 Province, and the eastern ]Joii:ion of the Wellington Pro'vinoe. 

 Where, however, the erosion of the covering strata is more 

 advanced in the higher eleivatecl blocks there are exposed areas 

 of the planed surface of the under-mass, which now appear 

 as portions of a " stripped peneplain," of which the further 

 reduction is very slow compared Vith that of the covering 

 strata. (See Fig. 10.) "An enormous amount of waste 

 results from the stripping of back-slopes, and dissection of 

 faulted and folded fronts. Exceptionally such waste may be 

 all removed as it is supplied, but in most places, deep 

 aggradation of troughs will take place progressively with the de- 

 formation, and with the degradation and dissection of the higher 



Fig. 10. Diagram to illustrate the origin of the present topography of New Zealand. 



A. Block-faulting resulting from the Karkouri orogeny. (For even clearness sake 

 this has been drawn as if no erosion occurred during the period of crust- 

 movement.) 



B. Jlodern topogiaphy resulting from removal by erosion of the softer covering-strata 

 from the resistant under-mass of the crust-blocks. 



1084.— 11 



