Speight. — Orientation of the Biver-valleys of Canterbury. 143 



the Rakaia, at the mouth of the Acheron River, near the Harper River, 

 and at Mount Algidus give little idea of structural peculiarities which may- 

 find expression in the shape and position of these river-valleys. 



When we cross into the Waimakariri basin we find the same arrange- 

 ment of parallel valleys in the country between Broken River and the Cass. 

 Taking the most westerly first, there are the following : (1) The valley 

 occupied by Winding Creek and Lakes Pearson and Grasmere ; (2) the 

 valley occupied by Sloven's Creek and its continuation following the line 

 of railway over St. Bernard Saddle to Lake Sarah and the Cass ; (3) the 

 valley of the Waimakariri. 



The directions of the first two of these are certainly determined by 

 structural features— at all events, in their lower portions. In Winding 

 Creek the Tertiary coal-measures form a strip along the floor towards the 

 junction with Broken River, and these have been folded with an axis rim- 

 ning along the line of the valley to the north-west. Again, in Sloven's 

 Creek there is a strip of Tertiary sedimentaries and associated volcanics 

 with a north-west strike and a south-west dip which has been tilted and 

 faulted down, and has certainly determined the direction of the valley in 

 its lower reaches. Whether in both these cases the fractures continue 

 north-west past the last exposures of Tertiary beds is quite imcertain ; but 

 it is extremely probable that it is so, the soft strata having been removed 

 from the higher parts of the valleys by the increased intensity of erosive 

 agents. There are no Tertiary sedimentary beds in the valley of the main 

 Waimakariri indicating any line of structural weakness which may have 

 determined its direction ; but just opposite the point where the Esk River 

 joins it there is proof of a dislocation running up the valley of the tributary 

 in a north-easterly direction, the Tertiary sediments being subjected to 

 folds on that line with a fault running up the western flanks of the Puke- 

 teraki Range in that region, tilting the sedimentaries along its line, and 

 determining the direction of the valley either by the channel being formed 

 by the fault-line or by depressing a strip of soft and easily eroded beds. 

 This is the only marked structural line of weakness running north-east, 

 but it is probably continued to the south-west toward the Castle Hill basin, 

 and in the valley of Coleridge Creek, which leads towards Coleridge Pass, 

 in the extreme south-west of the basin, we have a well-marked fault-line 

 where the dislocation can be positively seen in the markedly different levels 

 of beds dipping in the same direction on opposite sides of the valley. 



We see, therefore, that, while certain subordinate valleys do show indi- 

 cations of their directions being dependent on deformations of the strata, 

 the main vallej^s have not furnished any positive evidence of such ; but this 

 does not negative the statement that valley-directions are dependent in some 

 way on such a cause. They may be lines of earth-fracture. It will be 

 noted, however, that those cases which I have cited have a general noi1;h- 

 westerly trend, whether they are in the Rangitata, the Rakaia, or the Wai- 

 makariri basin, and do not correspond with the lines suggested by Dobson. 

 This divergence is most marked in the Waimakariri basin, for, while the 

 map of fractures suggested by that author would make the direction of the 

 upper Waimakariri almost east-and-west, the valleys whicli are dependent 

 on fractures in that region run N.N.W.-S.S.E. ; but itisnot impossible that 

 both sets exist, only there is positive evidence of the latter and not of the 

 former. The chief difficulty in detecting fault-lines in the mountain region 

 of Canterbury is that the rocks are of such a monotonous nature, with no 

 well-defined zones of distinctive lithological character or beds which can be 



