150 Transactions. 



with slight diminution up-stream almost to tlie mouth of the Crow River, 

 about four miles above the incoming of the Bealey River. When one also 

 regards the flare of the valley -walls the actual volume of the basin becomes 

 more impressive. It is no doubt true that this great basin has been en- 

 larged to its present size through the abrasive and excavating power of 

 the ice ; but during the ice-flood it would act as a great collecting gromid, 

 and materially contribute to the maintenance of the supply of ice, the 

 depth of which, judging from the evidence of ice-action on the valley- 

 walls, must have reached nearly 2,500 ft., even if it did not exceed it, 

 and have covered all the slopes almost to the grass-line. 



As this great body moved east it received notable additions from the 

 Hawdon Valley and from Andrews Valley, and at the same time the cross- 

 section of the main valley was much reduced. Hence, driven by the 

 weight of the ice above it and forced south by the tributaries coming 

 in from the north, it crowded over the Mount Misery -Cass Ridge and 

 entered the territory belonging to the valleys lying to the west of the 

 main Waimakariri, lowering the divide continuously by erosion. (See map.) 

 The tendency of such overriding flows of ice to cut distinct channels is 

 well illustrated in the notches in the ridge just mentioned, the upper ones 

 formed at the height of the ice-flood, and the lower one at the Cass Saddle 

 being formed throughout the whole period during which the ice was enabled 

 to surmount that portion of the ridge. Hence it is that the effects of ice 

 are so noticeable in its vicinity, for the erosive action would be very great 

 at that spot. The semi-detached knob which terminates this ridge, and 

 round which the railway goes from the Cass Valley to that of the main 

 Waimakariri, is the remnant of the ridge which has escaped destruction 

 when the overflow cut in behind it. It belongs to one of the " beehive " 

 forms common in glaciated regions where spurs have been semi-truncated. 

 The direction of the movement of ice is shown by that of the striae, and 

 also by the slope of the ridges between Mount Horrible and the Cass River. 

 In the basin which lies immediately to the west of the river these trailing 

 spurs all slope down from the north, even against the flow of the Cass 

 River, and discharge their surplus water south. This peculiarity can be 

 attributed chiefly to the action of ice scouring out channels and leaving 

 ridges pointing in that direction. 



The disturbance in the regular and even flow of the ice-stream where it 

 overrode the end of the Cass spur would be very great indeed, and this 

 would be intensified by the stream from the Hawdon coming in at right 

 angles from the north. The effect would closely resemble the eddies or 

 whirlpools seen under similar circumstances in a river. It seems that a 

 great ice eddy occurred between the Cass Saddle and the northern end of 

 the Sugarloaf, and this scoured out a great roundish pothole. A similar 

 landscape form is seen at the junction of the Lake Stream with the Rakaia, 

 formed under exactly similar conditions, but its shape is "more circular. 

 In this case, too, a narrow rock}" ridge had been left at the outlet of the 

 tributary stream which it has subsequently cut through. The marked 

 similarity of the two cases suggests more than a mere coincidence in shape. 

 It is probable, then, that a rockbound hollow marked the site of the 

 junction of the Cass with the Waimakariri, and when the ice retreated 

 this formed a lake divided from the main stream by a rock bar. (See 

 Plate XV, fig. 1.) 



The flooding of the country with ice in the direction of the Broken 

 ^iver is responsible for all the glacial features indicated previoush' ; 



