On a Remnant of a Stripped Peneplain of Palaeozoic Age at Mount Sedgwick in VVestern Tasmania

It is well e~tablished (Nye and Blake, 1938, pp. 22, 42) that a peneplain existed over much of Tasmania at the beginning of the Permo-Carboniferous sedimentation. Beds of Permo-Carboniferous and Trias-Jura sediments were laid down on this surface, and, apart from tilting, retain their original horizontal relation8. At, or near, the close of the Trias--.Jura sedimentation, the intrusion of a dolerite magma occurred on a widespread scale, forming huge dykes and ~ills. The sills were confined to the horizontally bedded strata, or to the plane of '~8eakness at their base where they rested on the surface of the peneplain. It is not known whether this peneplain extended to Western Tasrnania, or whether it gave place to an irregular erosion surface in that region. The distribu·· tion of the Permo-Carboniferous rocks (see below) makes it clear that, even in the latter case, the irregularities of the erosion surface were nothing like as great as those t'xisting to-day. This view is implicit in the opinion of Loftus Hills (19lt1, p. 25) that at one period 'the central plateau was practically continuous with the \Vest Coast Range, which did not then exist as a separate mountain range'