70 



T ransactions. 



floors at various lieiglits forming flat-topped and terraced hills, which 

 have been noted by many observers, throughout the three- to four-mile- 

 wide valley lowland, indicating that the Aorere has wandered widely on 

 a bruad flood-plain more than once during the excavation of its valley 

 in the covering strata of the fault-angle. It would appear that, after 

 the movements of deformation by which the major topographic features 

 were blocked out, the whole region stood some hundreds of feet lower 

 than at present, and tliat while the land was in this attitude there 

 occurred the great denudation which resulted in the removal of a great 

 part of the covering strata from the upland areas and the carving of the 

 blocks into forms approximating to those of tlie present day. It is 

 possible that the sea entered the north-eastern end of the fault-angle ; 

 but, if such was the case, the re-entrant so formed was no doubt rapidly 

 filled up, and at the same time a considerable amount of aggradation 

 must have taken place throughout the lower parts of the depression. 

 The traces of any such filling have been since removed by erosion. It 

 is a safe assumption that towards the end of the great denudation the 

 Aoi'ere River was not (Uily graded, but liad developed a flood-plain with 

 a width of about four miles, of which tlie highest terraces are remnants. 

 The lower terraces and the present valley of the river, with its discon- 

 tinuous narrow flood-plain, are to be ascribed to excavation by the 

 Aorere and its tributaries during recent intermittent movements of 

 uplift. 



The Gouland Downs Depressio?v\ 



As stated on an earlier page, the Aorere-Gouland depression is con- 

 tinued beyond the divide between the Aorere Valley system and the 

 streams flowing westward to the Tasman Sea. The south-westward con- 

 tinuation, though ol)viously cognate with the Aorere Valley portion, differs 



Fig. 7. — The Gouland Downs, showing the Slate Range on the 



from it so much in certain jjarticulars that it demands separate descrijj- 

 tion. Ihe floor, known as the Gotiland Downs, is in most respects 

 homologous with tlie sloping plateau of the Aorere Valley, while the 

 true boundary of the depression on the north-western side is a scarp 

 which, after an interrtiption, continues the line of the Wakamarama 

 fault-scarp. A subsidiary tilted block, the Slate Range, however, at the 

 base of and parallel with the Wakamarama Range, separates the latter 

 from the nearly level floor of the depression, Avhich is bounded on the 

 north by the fault-scarp fi-ont of tlie Slate Range block. 



The Floor. 



The stirface of the " downs " jjlateau (with an area of about twelve 

 square miles) is a plain of erosion similar to that forming the sloping 



