142 Transactions. 



reverse direction. As the river passes from the youthful to the mature 

 stage these abrupt right-angled turns will get smoothed out, and the control 

 of rock-structure on the direction may be difficult, if not impossible, to 

 determine ; and specially will this be the case in a country where the direction 

 of the strike, and with it that of the joints, is continually changing, even 

 if we leave out of consideration the disturbing efiect of another set of j jints 

 crossing at an angle approaching half a right angle. Thus it is that any 

 attempt to correlate our river-directions with the smaller rock structures 

 will lead to doubtful result, although they have really had a dominating 

 efiect in the beginning. 



Although Dobson states that the directions of the river-valleys was 

 probably due to a series of earth-fractures, he did not submit positive proof 

 of their existence, and I am unaware that any direct evidence has been 

 forthcoming since he wrote his report with regard to the main valleys. 

 In the case of some of the subordinate valleys there is, however, positive 

 evidence of the presence of structural features controlling their direction. 



In the valley of the Potts River, a tributary of the Rangitata, there is 

 an outlier of coal-measures whose stiike runs north-west parallel to the 

 direction of the valley, and the coal-measures have been faulted down on 

 a line running in this direction. This is altogether difierent from that of the 

 strike of the greywackes in the locality, which runs approximately north- 

 east. It appears, therefore, that there is an agreement with the line of fault 

 in the direction of the valley. The valley has been enlarged by glaciation 

 tni its upper portion has become a typical glacial trough, but it is blocked 

 at the lower end by a bar of greywacke through which the river lias cut a 

 gorge 600 ft. deep, where the effects of joints on the direction of short reaches 

 is very apparent. This gorge exhibits for a length of about three miles a 

 series of right-angled zigzags, one set of directions corresponding to the 

 strike of the beds and the other to the cross-joints, the general trend of the 

 gorge being, however, nearly at right angles to the line of the upper glaciated 

 valley. Similarly, in the high country between Lake Heron and the Upper 

 Cameron River there is an analogous occurrence of coal-measures, and, 

 although no large valley rims north-west in association with them, small 

 tributaries of the Cameron, together with well-marked landscape features 

 such as blufis, which may well be fault-scarps, and a series of peculiar 

 depressions, follow closely the line of dislocation. This direction is parallel 

 to that of the Lake Heron Valley, and remnants of Tertiary beds which are 

 left in it are folded in places on a N.W.-S.E. line. 



When we cros^ the Rakaia and consider the country in the neighbour- 

 hood of Lake Coleridge we find a series of five parallel valleys lying with a 

 N.W.-S.E. direction (see map). These are — (1) The main Rakaia, between 

 the gorge and Double Hill, boimded on the west by Mount Hutt and the 

 Palmer Range ; (2) the Lake Coleridge Valley, with its extension up the 

 Wilberforce ; (3) the valley through which the road passes from the southern 

 end of Lake Coleridge to the Harper River, in which lie numerous small lakes, 

 such as Georgina, Eveleen, Selfe, and which is separated from the Lake 

 Coleridge Valley by Kaka Hill and Cotton's Sheep Range ; (4) a valley 

 to the north-east of this, at a much higher level towards the southern 

 end of Lake Coleridge but specially well defined towards the Harper 

 River, in which lies Lake Catherine, the valley being continued across the 

 Harper up the Avoca River ; (5) another valley, of small size, lying right 

 against the western base of Mount Enys and the ridge rimning south-east 

 fi'om it. The remnants of Tertiary beds which exist at Redclifi Gully, on 



