60 Transactions. 



or geography of New Zealand, it is bv no means altogether new. It 

 was clearly in the mind of McKay as early as li^83,* and it is implied 

 in the descriptions of various areas in Nelson and Westland made during 

 the last decade by Henderson, Morgan, Webb, and others. 



The structure of tlie younger rock formations, where these have been 

 preserved, affords ample confirmation of this explanation of the relief. 

 Most of the larger relief features are tectonic forms — of course modified 

 by erosion to a great<^r or less extent — while the river-courses are very 

 largely consequent, still following very closely the courses taken upon 

 tlie tuml:)k'd and irregular surface j^roduced by a late disorderly uplift. 



In many cases the l)locks or units of the disorderly tumbled crust 

 are bounded by faults, lliis is, however, by no means universally 

 true, and where either formeidy horizontal strata — that is to say, hori- 

 zontally deposited strata which ai'e so young that they must be supposed 

 to have lain in their original horizontal attitude in the period imme- 

 diately preceding, tluit of uplift — or formerly horizontal, planed surfaces 

 are present, these frequently exhibit evidence of considerable deforma- 

 tion l)v folding. In some parts of the country, indeed, the intense 

 folding and mashing that the young strata have undergone jioint to 

 .strong compression accompanying — j^erhaps initiating — the movements. 

 In other parts, however, such evidence is lacking, formerly horizontal 

 strata and planed surfaces remaining flat, though frequently tilted, 

 over considerable areas. In the present state of our knowledge it can- 

 not l)e stated whetlier normal or reverse faults predominate. Xo attempt 

 will lie made in this paper to explain the cause of any earth-movements, 

 but attention will be directed to their effects as seen in tlie present form 

 of the land-surface. 



Xew Zealafid may be described as a concourse of earth-blocks of vary- 

 ing size and shape, in places compressed, the highest blocks lying in tlie 

 north-east and south-west axis of the land-mass, so that the whole struc- 

 ture ma}' be termed a geanticline; the blocks initially consisting of 

 an undermass of generally complex structure much denuded and largely 

 planed, and covered over jnost of the area by an overmass Aviiich liad 

 not been disturbed before the "blocking" movements took place; the 

 whole since the movements considerably modiiied b}- both degradation and 

 aggradation. 



In the present paper, a sketch of but a small portion of the NeAv 

 Zealand area, the writer cannot hope to demonstrate the accuracy of 

 tlie foregoing general description, but it is offered as a working hypothesis 

 which gives much assistance in the interpretation of this particular 

 district. 



X'ORTHERN XelSON. 



In the north-western corner of the South Island two fault-angle 

 depressions, the Aoreie and Takaka Valleys (see fig. 1), oj^en out broadly 

 towards the north-east and north, separating three composite upland 

 l)locks which, owing to diminishing throw of the boundary faults and 

 consequent dwindling of the fault-angle depressions towards the south- 

 west, coalesce in tliat direction. The north-western, or Wakamarama, 

 block presents a fault-scar}) front, but little dissected, towards the Aorere 

 Valley, while north-Avestward its back slope, much dissected by conse- 



* A. McKcay, " On the Origin of the Old Lake Basins of Central Otago," Geol. Surv. 

 of N.Z., Rep. (ieol. Expl. dur. 1883-84, pp. 76-81, 1884 ; see also " On the Geology of 

 Marlborough and South-east Nelson," ibid., 1890-91, pp. 1-28, 1892. 



