History of New Zealand. 315 
basin and are largely covered by young fluviatile gravel. Numerous 
other similar but smaller structural basins occur, the covering strata 
within which are more or less eroded or buried under fluviatile gravel 
according to their position with respect to local base-levels. It is 
evident that here, as in Marlborough, faulting has been accompanied, 
if not actually brought about, by a compressive force, for the covering 
strata are thrown into folds. 
From some of the uplifted blocks the surfaces of which were merely 
tilted slightly from their former horizontal attitude little below the 
base of the cover has been removed by erosion, and remnants are thus 
preserved of the fossil denudation plain which, in places at least, 
forms the floor of the cover. As an example the western slope of 
Mt. Grey may be cited. Farther to the south-west the outer 
ranges of the Southern Alps are composed of irregularly uplifted 
blocks, upon the tops of which are preserved remnants of a surface of 
small relief possibly also stripped of a cover. 
In the Oamaru district the base of the covering strata is of early 
Tertiary age, and the beds le upon a plane-denuded surface of 
the oldermass. There is less evidence of compressive stress here 
accompanying the Kaikoura movements, but the beds are thrown into 
broad folds. The open-water character of the sediments of the cover 
and the absence of coarse clastics are sufficient to show that the 
mountains to the west, into the valleys of which the covering strata 
now penetrate, were not in existence as a high land-mass during the 
period of deposition. ‘The structure and physiography suggest that 
the cover had formerly a great westward extension, and this is 
proved by their occurrence as narrow strips in trough depressions, 
-e.g. in the Shag and Waitaki Valleys. An account of the structure 
of an in-faulted outlier of the cover at Wharekuri, Waitaki Valley, 
has recently been given by Marshall.' Inland occurrences of the 
Tertiary rocks are thus easily explicable, and the theory of their 
. deposition in fiord-like arms of the sea, which was advocated for so 
long by Hutton, must now be regarded as definitely abandoned. 
In the Oamaru district large, gently sloping, flat areas of the fossil 
denudation plain forming the floor of the covering strata have been 
stripped but not destroyed. Some are seen to dip beneath the outcrops 
of the cover, as, for instance, south-west of Oamaru, and also in the 
Waihao basin north of Oamaru, where the presence of such a surface 
has been noted by Thomson? (see Fig. 2). Others occur on the tops 
of high mountain blocks differentially uplifted and tilted in various 
directions. Other and larger portions of the high blocks have 
been maturely dissected, and dissected fault-scarps are of common 
occurrence. 
Farther to the west, in Central Otago, the landscape is a mosaic of 
blocks the general nature of which has been recognized by McKay? 
1 P. Marshall, ‘‘ Cainozoic Fossils from Oamaru’’: Trans. N.Z. Inst., 
vol. xlvii, pp. 380-1, 1915. 
2 J. A. Thomson, ‘‘ Coal Prospects of the Waimate District, South Canter- 
bury’’: Highth Ann. Rep. Geol. Surv., 1914, p. 160. - 
3 “* On the Origin of the Old Lake-basins of Central Otago ’’: Col. Mus. and 
Geol. Surv. N.Z., Rep. Geol. Expl. 1883-4, pp. 76-81, 1884 (p. 80). 
