The Waitaki Graben.

The Waitaki River is consequent on the Kaikoura deformation. The middle and lower Waitaki follow a straight course in an east-south-east direction through a somewhat complex graben between the highland blocks of North Otago and those of South Canterbury. Its tributary the Haka-taramea enters from a great northerly-trending fault-angle depression.

In the Waitaki graben there are several small blocks of great interest as examples of tectonic forms. One small tilted block just behind Kurow exhibits an almost perfectly preserved back-slope and even crest-line (see fig. 3).

Fig. 3.—Small tilted block in the Waitaki Valley graben. View looking south-westward across the bed of the Waitaki River. The height of the scarp at the eastern end is about 1,000 ft. At the western end a glimpse is caught of the crest-line of the northern highland of Otago.

Another striking feature is a splinter from the northern fault-scarp of the graben just opposite Duntroon (Plate XXX, fig. 2). The fossil plain or stripped surface of the greywacke undermass, which is similar to that of the back-slope of the Hunter's Hills,^* forms a plateau considerably over 1,000 ft. above the level of the valley-floor, and a strip of it descends in a westerly direction along the splinter, coming right down to the level of the low terraces bordering the river. While the cover has been removed, the fossil plain is almost untouched by erosion. The fault-scarp at the back of the splinter is well preserved; that in the front has been sharpened by the river.