REPORTS OF COMMITTEES. 287 



The following conclusions were come to as the result of detailed 

 observations : — 



(1) The truncation of spurs to a greater or less extent is apparent 

 in nearly all cases where lateral valleys join a main one. 



(2) This appears to be greatest where the tributary valley meets 

 the main valley nearly at right angles, or at an angle greater than a 

 right angle. 



(3) The cutting back is almost wholly on the down stream side 

 of the tributary. 



(4) When a portion of the spur still remains stretching out into 

 the valley (like a reef running out from a point), a deep notch sometimes 

 occurs close to the steep end of the truncated spur. Fm'ther out in 

 the valley the rocks rise higher. 



(5) There are sometimes a series of terraces produced by erosion 

 above the principal. face produced by cutting back. 



(6) All the rocks standing up above the floor of the valley show 

 strise and fiutings, thus showing that the truncation was the work of 

 ice. 



This striation is becoming much more apparent in the Waima- 

 kariri Valley, as the clearing of forest has shown that what were 

 previously considered moraines are in most cases the remnants of 

 truncated spurs. An excellent instance of rock striation is thus dis- 

 closed within a few yards of the Bealey Hotel, on the Christchurch- 

 Hokitika road. Other good illustrations of spur truncation are seen 

 in the valley of the Waimakariri at the junction of the Crow River, the 

 Bealey, the Hawdon River, and Dr. Cockayne, who accompanied one 

 expedition, tells me that the same phenomena are repeatedly seen 

 up the Poulter River — another tributary of the same river. Similar 

 phenomena were observed in the Rangitata Valley. 



I think it will be apparent that the truncation of the spurs is due 

 to great pressure, which must occur on the down-stream side of a tribu- 

 tary glacier when it joins the main stream. 0\\ang to the imperfect 

 fluidity of the ice and its slow motion^ the tributary glacier is forced 

 over the shoulder of the spur on its lower side. Its corrasive power 

 is very great, and the spur is being continually cut back, either by 

 sapping of the walls or by their being overriden by the ice. In the 

 second case a series of shelves may be cut out. As the spur is becoming 

 reduced to the level of the valley it is natural that erosive action will 

 be more intense near the end of the spur, and thus the notch will be 

 formed. 



It seems probable that the obscure terraces or zones of tolerably 

 even slope, which occur above the steep walled sides of valleys heavily 

 eroded by glacier action, may be put down at times to an action similar 

 to that which produces the terraces above truncated spm-s. These 

 shelves are frequently seen where the glacier has moved round the 

 shoulder of a hill, or in the narrower parts of the valley. Where the 

 valley widens out the slopes become more even, and such shelves are 

 absent. 



