Cotton. — Block Mountains and a "Fossil" Denudation Plain. 65 



these facts give strong support to the view that the Wakamarama Range is 

 the dissected remnant of a tilted bh^ck (or possibly a complex of minor 

 folded and faulted blocks which may in a general description be con- 

 veniently considered as a single block) presenting its front or scarp 

 to the Aorere Valley and its back slope to the Tasman Sea, a view in- 

 volving the not unreasonable assumption that the covering strata, lying 

 on a planed surface of the underniass, were continuous across the site 

 of the range prior to the uplift of the block, and that since the uplift 

 they have been more completely removed from the higher than from 

 the lower ground. 



As the foregoing assumption is contrary to the interpretation of the 

 geological history and physiography of the district given by Bell in 

 the Parapara bulletin to which reference has already been made, the 

 conclusions there arrived at may be also stated. According to Bell's 

 interpretation, maturely dissected mountains occupied the area in the 

 period immediately j^receding that in Avhich the covering strata were 

 laid down, and the period of deposition was one of only partial sub- 

 mergence. The unsubmerged mountains are regarded as still surviving 

 in a form but little altered, and, on account of their supposed relation 

 to the younger deposits, they are termed the "old land." While the 

 occurrence of some faulting and therefore of some differential movements 

 of later date than the period of submergence is recognized, the uplift 

 of the already mountainous " old land " to its present height is ascribed 

 mainlv to "bodily secular movement since the Miocene era" (pp. 21, 

 23-24). 



" The old land represents physiographically an ancient mountain- 

 range Avhich had probably been maturely dissected prior to Miocene 

 times. . . . One sees generall}- the rounded outlines so characteristic 

 of elevated land-surfaces subjected to long-continued subaerial erosion " 

 (p. 2.3). 



The North-eastern Portion of the Scarp. 



Towards the north-east, as on the north and north-west, the surface 

 of the Wakamarama block descends towards the sea, and maturely dis- 

 sected covering strata survive on it. The fault-scarp facing the Aorere 

 Valley decreases in height towards the north-east, therefore, and towards 

 the mouth of the Aorere Valley the covering strata make their appear- 

 ance on the crest of the range. The line of unconformable contact 

 between the undermass and the cover runs obliquely up the face of the 

 fault-scarp towards the south-west, but, unfortunately, owing to the 

 covering of forest, details of the contact are not easily seen. At first 

 sight it appears as though the even crest of the range on the undermass is 

 continued on the bevelled edges of the cover as in fig. 4. a. As there 

 can be little doubt that the even crest on the undermass is determined 

 by the resurrection of a denudation plain, this would mean the presence 

 of intersecting denudation plains, and would involve strong uncon- 

 formity between a lower series of conglomerates and coals* (those exposed 

 on the face of the scarp) and an upper series (also coal-bearing)t on 

 the back slope of the Wakamarama Range farther to the south-west. 

 As, however, the beds are all regarded by Park as belonging to one 

 conformable series, it is probable that the appearance of intersecting 

 denudation plains is false, arising from an increasing inclination 



* Described by Cox and Park in the papers previously referred to. 

 t Bell, k>c. cit., p. 55. 



3— Trans. 



