48 Transactions. 



The glaciated knobs of the Central Plateau of France that he notes 

 later on hardly come into this category, but on page 288 he refers to rocky 

 knobs seen in abundance about Ambleside and along the ridge separating 

 Thirlmere from St. John's Vale, in the County of Cumberland, in England. 

 In this paper he everywhere emphasizes the potency of glacier erosion, 

 especially in valleys. 



In a subsequent paper (1905, pp. 4-5) he again refers to knobs : " The 

 knobs and ledges may be taken to be so-many unfinished pieces of work, 

 which would have been more completely scoured away had the glacial 

 action lasted longer." This point he again emphasized in a paper on 

 " American Studies on Glacial Erosion " (1910, p. 423), and refers to it 

 slightly in the discussion on his account of the glacial features of North 

 Wales (1909), and also in an answer to a question on glacial knobs addressed 

 to him by M. Allorge. 



This is a summary of Professor Davis's position as far as I can see from 

 the literature at my disposal. It will be noted, however, that nowhere 

 in the papers I have cited has he illustrated his point by showing the various 

 stages by which a spur actually develops into a field of knobs ; and this is 

 somewhat surprising, as the method would be one entirely in keeping with 

 the way in which he so frequently presents a physiographic problem. 



I have examined other authorities, such as Hobbs and de Martonne, 

 and find that faceting is everywhere recognized, but no other forms are noted. 

 In the report of the Harriman Expedition to Alaska, G. K Gilbert deals 

 exhaustively with the origin of hanging valleys and faceted spurs, but 

 says little or nothing of any other of the various stages of modification 

 However, I have examined the maps and illustrations and can see little 

 evidence of intermediate forms, with the possible exception in the case 

 of Nunatak Glacier (p. 59, and map), where the Nunatak appears to be 

 a detached knob or end of a reduced spur. 



Since there is this absence of statements concerning intermediate forms, 

 I have attempted to supply some evidence as to their occurrence which I 

 have come across during years of intimate acquaintance with the alpine 

 region of the South Island of New Zealand. Incidentally this will be found 

 to support Davis's contention that fields of knobs in the floor of a glaciated 

 valley represent the remnants of spur-ends. 



The main effect of ice-action on valley-spurs is due to abrasion, although 

 no doubt plucking is very important at times, and especially in its more 

 mature stages, when the spur-ends have become faceted At this stage, 

 too, the excavating-power of a glacier has a dominating influence on the 

 resulting landscape-form. But the depth of the ice, its velocity, and the 

 time to which the surface has been subject to its action all exert important 

 influences ; and, further, the direction in which the tributary valley meets 

 the main valley also controls to some extent in its initial stages the result 

 of ice-action on the spur-ends. 



As its dominating influences are those of thickness, velocity, and time, 

 the modification of valleys, and therefore of the spurs running into them, 

 will be different in different parts of the valley, being more pronounced in 

 the upper portions, owing to the fact that these agencies are there at their 

 maximum. Those parts of the valley where the ice is thickest, its velocity 

 greatest, are just those parts which have experienced its action for longest 

 time, and therefore modifications will be carried further than in the lower 

 reaches. It will follow also that the character of the pre-glacial topography 

 will be most easily arrived at by a study at the fringe of the glaciated district, 



