Speight. — Loire?- Waipara Gorge. 225 



it must be noted that they are fully charged at the present time, and it 

 is quite conceivable that they could build up a shallow sea-bottom till it 

 was above sea-level without any change in the level of the land. I can- 

 not, however, think that this explanation is altogether satisfactory, and 

 conclude that a small and probably continuous uplift lias taken place 

 after a comparatively long period of stability, during which the old 

 coastal plain was eaten back to the line of the former sea-cliff. 



Judging from the profiles of the streams joining the Waipara from 

 the flanks of the Deans Range and elsewhere, this movement has extended 

 its effects some distance inland. The loops of the river in the gorge 

 itself, placed as they are in a somewhat narrow trench, may owe their 

 origin primarily to the fact that at a former period the river reached 

 base-level, and that the gorge was cut down to its present depth during 

 a subsequent period of elevation when the river had increased power to 

 corrade, and that now it has again almost adjusted its grade to the load 

 it carries, and all its erosive energy is devoted to destroying the loops 

 that it previously formed. It is very difficult, however, to correlate 

 these effects with certainty. 



Origin of the Waipara Gorge. 



The circumstances resulting in the formation of the Waipara Gorge 

 furnish one of those interesting problems with respect to drainage direc- 

 tions for which the North Canterbury district is noted. When the river 

 leaves the hills between Mount Brown and the Deans, and issues from the 

 middle gorge, whose existence has been largely determined by the great 

 Mid-Waipara fault, it pursues a course of about seven miles across the 

 Waipara Plains, and, instead of taking the easy path to the sea past 

 Amberley, it cuts a somewhat deep channel through the downs which 

 stretch south-west from the termination of the Limestone Range. Here 

 it runs practically along the strike of the beds which form this somewhat 

 elevated ground. At times it breaks across the strike for a short dis- 

 tance; still, the coincidence is very marked, even when the strike swings 

 round through a right angle. When the river leaves the downs and 

 debouches on to the coastal plain it pursues a direct course to the sea, 

 still following the strike approximately. There seems to be no reason 

 from the present configuration of the ground why this difficult path 

 should have been selected when an easy one was ready to hand, so that it 

 is apparently one of the instances of the anomalous behaviour of rivers 

 which the district furnishes. 



The Waiau and Hurunui, a few miles further north, and even the 

 Waipara itself in its upper portion, have cut gorges through mountains 

 composed of hard greywackes and slaty shales of Mesozoic age when they 

 might easily have avoided the obstructions. The only satisfactory ex- 

 planation is based on the fact that they are instances of " superimposed ' 

 drainage. In late Cretaceous and early Tertiary times an archipelago 

 of small islands formed of rocks of Lower Mesozoic age occupied the area 

 now known as North Canterbury and the Amuri districts. In the straits 

 and bays among these islands, greensands, solid limestones, marls, and 

 loose incoherent calcareous sands and gravels were laid down, so that 

 the original surface was completely masked. When the land was raised 

 above the sea in late Tertiary times the course of the streams established 

 upon it was largely determined by the form of the land as it emerged. 

 While cutting down their channels the streams removed a large part of 

 the veneer of loose and readily eroded material, encountered the hard 

 underlying rocks, cut into them, and maintained their original direc- 

 8- Tran-. 



