214 Transactions. 



the ancient folding. (An exceptional belt of shattering close to the city 

 of Wellington, which crosses the strike diagonally, is not here referred to. 

 It appears to be connected with fault movements of a much later date than 

 the folding of the rocks.*) 



The texture of the dissection on both the higher ridges of resistant rock 

 and the lower belts of subdued topography is somewhat fine, owing, no 

 doubt, to the low permeability of the mantle of residual clay that results 

 from the weathering of the greywacke. 



The development of the present mature topography seems to have been 

 interrupted from time to time by renewed uplift, as ' in the Wellington 

 peninsula farther to the south-west,")" but the high valley-floors of the earlier 

 cycles are here maturely dissected, and the land-forms of the various cycles 

 merge almost or quite completely into one another. Some of the later 

 pauses in the uplift are probably recorded by the fragmentary terraces in 

 some of the valleys. These are generally rock terraces, but some are formed 

 of alluvium — e.g., in tne Otaki valley a thick mass of fluviatile gravel 

 underlying a portion of a terrace and extending below the present level of 

 the river suggests trenching, due to uplift, and later refilling of the trench, 

 perhaps during a temporary submergence preceding an uplift to which the 

 cutting of the present narrow inner valley of the river is due. The terrace 

 features cannot be ascribed wholly to vertical movements of the land, how- 

 ever, for they must be closely connected with certain to-and-fro movements 

 of the shore-line which will be described below. 



The margin of the upland block is a mature coast-line rising in places 

 as high cliffs, but fronting the sea now only at the south-western end, 

 beyond the limits of the district here dealt with, and bordered elsewhere 

 by a coastal lowland the width of which increases north-eastward. With 

 respect to this lowland of later growth the upland block may be spoken of 

 as the " old land." The ancient coast-line of the old land appears to have 

 originated as a fault coast, for its almost straight north-east and south- 

 west trend crosses the grain of the country obliquely. Whatever the initial 

 form may have been, however, a mature coast of simple outline developed 

 by marine erosion now forms a nearly straight boundary-line between the 

 upland block or old land and the strongly contrasted coastal lowland. 



The Coastal Lowland. 



Different parts of the coastal lowland are of different ages, and their 

 present topographic forms have been developed in different ways, and the 

 materials of which they are composed, though in some cases originally 

 identical, are in different stages of consolidation and decay, so that they 

 yield very different soils. The materials also came originally from two 

 distinct sources. 



The divisions of the lowland are best introduced by a discussion of the 

 conditions under which it seems to have come into existence. All the 

 features of the lowland may have been produced by an alternation of retro- 

 gradation (or retreat of the shore-line under wave-attack) with progradation 

 (or advance of the shore-line due to accumulation of the waste of the land). 

 Such an alternation is necessarily connected with a fluctuation in the supply 



* C. A. Cotton, Supplementary Notes on Wellington Physiography, Trans. N.Z 

 Inst., vol. 46, pp. 294-98, 1914. 



t C. A. Cotton, Notes on Wellington Physiography, Trans. N.Z. Inst., vol. 44, 

 pp. 245-65, 1912. 



