20 Transactions. 



Apart from the glacier shelves there are no terraces, as in 

 this portion of their course the rivers are aggrading their beds. 

 The supply of waste is almost inexhaustible. It is poured in by 

 every tributary stream and every shingle-slip, and the grade 

 of the river is not sufficient for its transportation. Where the 

 tributaries are large, the result is to flatten the grade of the 

 main river above the junction and to push the main river over 

 to the opposite side of the valley. This effect is especially 

 marked in the case of the Bealey River. Surveys carried out 

 by Mr. Edward Dobson, C.E., when searching for the best route 

 to the West Coast, show undoubtedly that the grade of the 

 Waimakariri has been considerably modified, in the manner 

 suggested, by the action of this large tributary. The main 

 river is not competent to remove the load poured into it. 



This portion of the river-valley has been deepened bv glacier 

 erosion, though not to any great extent, as the roches moutonnees 

 in the Rangitata, Rakaia, and Waimakariri valleys show ; but 

 the rivers have no power now to form terraces, except very low 

 and temporary ones. 



The valleys at the head of Lakes Pukaki and Tekapo, in 

 the basin of the Waitaki, show the conditions which prevailed 

 in all the valleys in Canterbury after the maximum glaciation 

 was past. A lake occupied the Lower Rakaia Valley, ponded 

 back by a bar stretching across the mouth of the gorge ; a similar 

 lake filled the. Waimakariri Valley from the gorge as far as the 

 junction with the Hawdon River, if not farther, and in all pro- 

 bability one existed in the Rangitata. 



The formation of these lakes is due to one of two causes — 

 (1) to the elevation of the land along an axis which coincides 

 with the outer range forming the eastern boundary of the Southern 

 Alps ; or (2) to glacier erosion. 



Tf this axis of elevation really exists, it would be approximately 

 in a line with that running through the Kaikoura Mountains, 

 where crustal movements are now going on. This axis has, 

 without doubt, extended from the Kaikouras in a south-westerly 

 direction, and perhaps the great Waipara fault has been associated 

 with this earth-movement. The fault is of very recent date, 

 and coincides with the gorge of the Waipara River, and has a 

 downthrow to the north of over 1,000 ft. Unless this fault is 

 due to lateral movement, it is necessary that a thickness of 1,000 ft. 

 has been removed from rocks about the Weka Pass and Waipara 

 River, for the escarpment of the Mount Brown beds presents 

 a tolerably even line both north and south of the fault-line. 

 The physical features are more easily explained by a lateral 

 movement of the rocks, resulting in fracture along the jjorge of 

 the Waipara. The force producing this rupture must have come 



