Speight. — Modification of Spur-ends by Glaciation. 51 



to the forest-covered slopes near Manapouri ; but it is noteworthy that 

 erosion has reached a similar stage in each individual of the series of knobs, 

 suggesting that they were all formed by the same ice-flood, as is the case 

 of those near Manapouri. 



The fact that the series of notches in these spurs has been cut all at the 

 same time suggests that the shelves existing in valleys of the European 

 Alps may, in some cases, have been cut during one period of ice-advance. 

 These are referred to by de Martonne in his Geographic Physique (p. 641). 

 After describing the shoulders which are so characteristic of these valleys, 

 and the location of villages on them, he says, " Les replats multiples indiquent 

 que l'erosion des vallees alpines est le resultat d'une serie de phases d'erosion 

 glaciaire et d'erosion fluviale alternantes, produisant un enfoncement pro- 

 gressif du thalweg et im encaissement de plus en plus grand de la vallee, 

 malgre les efforts faits par le glacier pour reculer le pied du versant par 

 sapement a chaque periode glaciaire ! " Although it is dangerous to express 

 an opinion without having seen the locality, it seems possible that these flats 

 and shoulders may — in some cases, at all events — have been formed at one 

 glacial effort, like those at Manapouri. 



An important factor which affects the resulting form of the spur-remnant 

 is the angle at which the pre-glacial valley of the tributary meets that of 

 the primary. It will be most convenient to take the simple case when they 

 meet at right angles or nearly so. Good illustrations of this case are fur- 

 nished by the Bealey and Hawdon Valleys at their junction with that of 

 the Waimakariri. The two tributaries come in from the north, whereas the 

 main stream runs from west to east. The tributary valleys are subequal 

 in size, and the size of the glaciers issuing from them at the height of the 

 glaciation, judging from the present cross-section of the valleys, would be 

 about one-fourth of that of the main stream. As a result of the greater 

 weight of the ice in the main valley, the tributaries were crowded over the 

 shoulder of the spur on the down -stream side of the tributary, with the 

 result that they have both a flattish shelf about 100 ft. above the present 

 floor of the valley and about 200 yards in length, formed by the cutting-down 

 of the end of the spur, so that it terminated in a kind of platform analogous 

 to the wide shore-platforms sometimes seen off a point on a coast-line 

 composed of moderately soft rocks. (See Plate X, fig. 2.) The two spur- 

 ends are so similar in position, shape, and extent that they might easily be 

 mistaken, and photographs taken from the opposite bank of the Waimakariri 

 are almost interchangeable. The similarity in form is no doubt to be 

 attributed to similarity in the conditions under which the spur-ends were 

 reduced by the glaciers as erosive agents. 



If erosion proceeds further the shelf is cut down near its proximal end, 

 and the beehive form again results, but it is then flatter than that resulting 

 from the passage of the main stream at right angles over a trailing spur. 

 If the tributary meets the principal valley at an angle greater than a 

 right angle, as in the case of Harrison Arm and Milford Sound, or the Sinbad 

 Valley with Milford Sound, then the form becomes accentuated. The 

 formation, not of a shelf, but of the couchant-lion shape, takes place, 

 but ultimately this must develop into the beehive form. This form is, of 

 course, subject to profound abrasion, and is liable to be reduced by attack 

 from both sides and also on top, so that it ultimately becomes a mere 

 roche moutonnee, standing in the floor of a glacial trough, and apparently 

 without genetic connection with the valley-sides. In most cases, however, 

 such isolated rocks were once connected directly with the valley-sides, the 



