,"336 T rtnisactionx. 



connected Avith. Such ridges will generally lie parallel to the direction 

 of the ice-flow, and will be abraded and reduced in height if the ice can pass 

 over them, and reduced in length where it cannot pass over them. Thus all 

 stages appear between the long spur and the conical hill. In the valley of 

 the Waimakariri and in the Lake Coleridge basin on the north side of the 

 Eakaia River the intermediate forms occur in perfect sequence ; but in the 

 Lake Heron district the destruction has been more complete, and the spurs 

 grade into low flat roches moulonnees or into ice-planed slopes. An instance 

 of such a cut-out spur can be seen in Shaggy Hill, five miles north of Lake 

 Heron, where lay the original divide between the Ashburton and Eakaia 

 basins, which has been lowered, and one of the spurs reduced to an immense 

 rochc vwutonnee. An advanced stage in the destruction of such a ridge 

 occurs in the Sugarloaf, at Lake Heron. This mass is evidently the remains 

 of a spur which divided two valleys, and which projected above the stream 

 of ice as a nunatak even at its maximum, for its top shows no sign of 

 glaciation, while its sides and northern end \vA\e been rasped and smoothed 

 away. 



(/.) Valley -features. 



The profiles and cross-sections of the valleys are those produced by 

 the action of glaciers on a matured stream system. Their special features, 

 such as the alignment of the valley-walls, the trimcation of the spurs, and 

 the presence of glacier-shelves, roches moutonnees, and moraines, have been 

 just dealt with. The surface features of the Lake Heron Valley have been 

 little altered since the glaciation, and this suggests that it cannot have 

 occurred at a distant period of lime, geologically speaking. The Rakaia 

 Valley has been subject to the action of a great river overcharged with 

 detrital matter, so that the U-shaped floor has been filled to considerable 

 depth with material derived from the glaciers at its head and from tributary 

 streams and shingle-slips. The U-shaped form has thus been modified 

 and the floor has been flattened by the deposits of an aggrading stream. 

 The actual depth of the deposit is unknov/n at present, but it must amount 

 ill places in hmidreds of feet. 



The cross-sections of the valleys present some interesting features. 

 Above the level of the truncated spurs, or above the level to which the 

 glaciers filled the valleys — and this applies to the tributaries with equal 

 force — the slopes become concave in shape (Plate VI, fig. J). These are to 

 be found in the whole mountain area of Canterbury. At higher levels they 

 are occupied for a part of the year with snow, and they seem to owe their 

 origm to its weathering action. By its presence the surface of the rocks 

 is maintained in a moist condition, and slow but sure chemical and other 

 erosion takes place, a shell-like hollow being eventually formed. The snow 

 forms these hollows, in which afterwards, as weathering action proceeds, 

 thick drifts accumulate. If the climate grows more rigorous or other cir- 

 cumstances promote the progressive accumulation of snow, then a small 

 glacier forms. Such conchoidal slopes, developed under former more severe 

 climatic conditions, are the favourite location of our moisture-loving alpine 

 plants and our mountain meadows, with their rich displays of Ramincidus 

 and Ourisia. 



(g.) Carrie Glaciers in Relation to the Formation of Passes ami the Dissec- 

 tion of Spurs. 



In former times, when the conditions favoured the accumulation of 

 thick drifts of snow, these concave hollows were gradually filled with ice 



