52 - Transactions. 



connecting ridges having been completely removed by glacial abrasion. All 

 the different stages in the formation of such isolated rocks from spur-ends 

 can be seen in the valleys of the Southern Alps. 



Worthy of special mention are the detached hills which lie in the angle 

 between the Poulter and Esk Rivers near their junction with the Wai- 

 makariri. They are the remnants of the spur which once came down 

 between the two former rivers, and whose end was dismembered by the 

 large glaciers which issued from the Poulter Valley and Boundary Creek 

 Y'alley, crossing it near its termination. 



Spurs are eroded on the up-stream side in a somewhat different way. 

 There is no overriding except in the case of the main stream entering a 

 distributory valley, as in the case of the Rakaia branching off into the Lake 

 Heron Valley, or when a glacier crosses the mouth of a tributary valley 

 which is bare of ice. When, however, both are full of ice the end of the 

 spur is modified by an action which is analogous to the whirlpool that 

 forms when two rivers join, as a result of which the end of the spur is 

 ground back below the surface of the glacier, so that it presents a steep 

 face at the angle between the streams. 



When the tributary meets the main valley at an argle less than a right 

 angle the spur-ends are cut back, though with less overriding of the end 

 than when the angle is greater. Narrow shelves, somewhat resembling 

 terraces, are the common resultant form. Excellent illustrations of these 

 can be seen at the junction of the Macaulay River with the Godley, and in 

 the angle between the Potts and the Rangitata. 



When valleys are subparallel, then there can be little or no truncation 

 of the dividing ridges, but these are dismembered and cut into lengths as 

 the result of lateral corrasion, chiefly by means of small tributary glaciers 

 of the corrie type whose heads ultimately meet and 'ower the divide. Thus 

 we get the elongated rocky hills which are so frequent in our ice-enlarged 

 intermontane basins, which if submerged would produce elongated islands 

 in parallel or linear arrangement, such as those which add to the scenu 

 beauty of the West Coast Sounds, notably Dusky and Doubtful Sounds. 



In the figures given by Davis illustrating partially destroyed spurs, 

 fields of knobs appear to be a common feature. I have noticed occurrences 

 similar to these in places where spurs have been partially destroyed — e.g.. 

 in the valley of the Harper River to the north-east of Lake Coleridge ; but 

 the most characteristic occurrence is in the valley of the Rangitata at the 

 place called by the somewhat striking name of the " Jumped-up Downs." 

 (Plate XI, figs. 1 and 2.) This is evidently the residual of a destroyed spur, 

 and its irregular appearance is well described by the name given by the ear v 

 settlers. Right out in the floor of the Rangitata Valley is an isolated rocky 

 mound in a line with the hummocky area ; this is evidently the remnant 

 of a spur which reached a considerable distance into the wide basin now 

 occupied by the river. 



The surface of these hummocks is characteristically worn into smaller 

 roches moutonnees, often well striated, forming rounded oval masses with 

 dimple-like hollows in between. When the general surface is flat, as is 

 frequently the case when shelves are formed from the terminations of spurs, 

 shallow rock-bound pools are formed containing the characteristic bog- 

 vegetation of these regions, which passes into peaty masses. Excellent 

 examples of these can be seen on the platforms at the junction of the 

 Bealey River with the Waimakariri, and on the reduced spur-ends farther 

 up-stream opposite the mouth of the Crow River. 



