Geological Structure And Topography. The most striking feature of the general topography as seen from any high peak within this region is the general accordance of the summit level (see Plate 1 and Plate 3, Fig. a.). Though early recognised by Andrews (1905) as resulting from peneplanation, this accordance has since been discussed in greater detail (Benson, Bartrum and King, 1935, Benson, 1935a), the whole Fiordland region being described in explanatory terms as an elevated subdued matureland, which has been thoroughly dissected and subsequently heavily glaciated. That the region was not in a very advanced state of peneplanation immediately prior to the uplift which made possible the deep dissection, seems to be indicated by the forms of the higher mountain-shoulders, the presence of a rather broad and shallow matured upland valley at the head of the Seaforth River between Lake Manapouri and Dusky Sound (described and illustrated by Wilmot, 1897), and the degree of irregularity among the summit-levels. The last factor is, however, of less significance, being influenced by the headward erosion of streams in the new cycle. There is not sufficient evidence to indicate whether the initial unevenness of surface was the result of mature erosion following an uplift of a few hundred feet only of what had been a surface produced by advanced peneplanation—a suggestion which seems to accord with the features of the Upper Seaforth River—or merely an incomplete single-cycle peneplanation occurring during Late Tertiary times after the Mid-Tertiary (Miocene ?) crustal dislocation (cf. Benson, 1935a). Long prior to such dislocation, however, the Fiordland crust-block had been broken by a series of intersecting master-joints, fault-zones and shatter-belts, and such lines of weakness clearly guided the direction of valleys cut both during and after the Late Tertiary peneplanation. Moreover, they were revived during the differential crust-movements, formation of horsts and graben—or fault-angle troughs—which accompanied the Late Tertiary-Pleistocene elevation. (Benson, 1933, 1935). Such ancient “lineaments” (cf. Hobbs, 1911) are very distinct in the Preservation Inlet area, 140 miles south-south-west of the present region, and some of those therein represented are in evidence in the region here discussed. Thus the Lower Hollyford Valley and Lake McKerrow, the Right Branch of the Routeburn, the Upper Rockburn, the Lower Beansburn, the Dredgeburn, most of the Lower Dart Valley, the Earnslaw Burn, the Lower Rees Valley, the Upper Shotover, and the upper part of the West Branch of the Matukituki Valley appear to follow zones of structural weakness which trend in a direction slightly west of north (cf. the Acheron Passage in Dusky Sound). Valleys trending north-north-east to north-east (compare Edwardson and Long Sounds and the general trend of the coast of Fiordland) are represented by Lake Alabaster, the Pyke Valley, the peridotite intrusion, the Upper Olivine and Hidden Falls Valleys, the Upper Beansburn, the Middle Dart Valley, the Upper Rees Valley, upper part of Snowy Creek, the Dart and Snow-white Glaciers, the Upper Waipara, Joe, Williamson and Arawata Rivers, and the Ice Plateau on the flanks of