258 Transactions. 



Judging from the shape of the floors of the Sotmds, from their con- 

 stricted and shallow entrances, with, in certain cases, shallower water in the 

 open sea, it seems certain that glaciers have enormous power of excavation. 

 It is possible that more exact soundings may show a continuance of some 

 of the valleys seaward across the submarine shelf. Depths exceeding 

 300 fathoms are foimd immediately off the entrance to some of the Somids 

 on a sea-floor which averages less than 100 fathoms deep. It seems hardly 

 necessary, however, to postulate enormous thicknesses of ice to perform the 

 work. Because ice-action is seen on the sides of an ice-eroded valley high 

 up above its floor, it no more proves that ice filled the valley up to that 

 level than high river-terraces prove that the river formerly filled the valley 

 from its present channel up to those levels. Ice has power to produce rock- 

 cut terraces which are analogous to stream-cut terraces of primary excava- 

 tion (I have seen instances in the glaciers of the Southern Alps), and many 

 of the signs of glacier-ice high above present vaUey-floors are relics of the 

 action of the ice streams when they ran at a higher level. The evidence 

 for the existence of glaciers five and six thousand feet thick sometimes 

 demanded in such cases as this seems to me to be very weak, and such 

 enormous thiclcnesses are quite unnecessary in order to produce the results 

 achieved. 



There are one or two land-forms, however, which result from glacier 

 erosion of a former well-developed valley which I do not remember to have 

 seen noticed previously. The first is the special shape of the ends of 

 truncated spurs. These are almost invariably cut ofi, and reduced to a 

 facet. The uniformity and regiilarity of this shape is striking. This can 

 be seen very well indeed in the broader Sounds, where the pre-glacial valley- 

 sides were not so steep, were more regular, and where the planing action 

 of the ice was not so intense. The phenomenon is almost absent in Milford. 

 I have seen it well marked in some of the valleys of Canterbury, where 

 the pre-glacial drainage system was more mature. The spur sometimes 

 shows that truncation was repeated, and that, after one strip had been 

 planed ofE, another one was begun, and a shelf or terrace left half-way up 

 the facet. These faceted spurs seem to be stable landscape forms, and 

 persist when other signs of glaciation aie disappearing. They do not receive 

 any drainage except that which falls directly on their surface, and from their 

 even nature it is long before streams estabhsh themselves on them. When 

 streams do, they are usually straight, and take the most direct course down- 

 hill, and for this reason they are numerous and small. All this tends to per- 

 petuate the original form of the facet. These truncated spurs are formed in a 

 moderately mature drainage system where the lateral spurs are not strongly 

 developed, and the axis of the valley is tolerably straight. When the direc- 

 tion of the valley is subject to marked variations, and tm'ns through an 

 angle approaching a right angle, then the ice overrides the spur. If 

 the angle turned is gxeater than a right angle, the action is still more 

 marked, and crouching-hon forms ensue. One feature resulting from this 

 action is that of a rounded hill lying of? the end of a spur. This has 

 been moulded by the erosive action, which is more marked near the 

 valley-wall, so that a deep notch is sometimes formed behind the knob. 

 Some of the isolated rounded hills and rocks found in glaciated comitries 

 may arise in this way, but many must result from the destruction of 

 longitudinal spurs dividing adjacent subparallel valleys. Transitional forms 

 in all states of development can be seen in the mountain district of Canter- 

 bury, 



