96 Transactions. 
level, and, given time enough, extends it headward until a flat-bottom 
trench is produced. Should the glacier then melt, a hanging valley would 
be left, the mouth of which would open out on the slope on which the 
glacier originated.” This statement seems to fit the conditions here 
admirably ; but in the case under consideration the backward sapping 
will be more rapid if carried on along the strike of beds of structural or 
lithological weakness. 
n important circumstance to consider is the cause which determines 
the height at which hanging valleys lie above the floor of the main valley. 
If they are to be attributed to overdeepening of the main valley or to 
cutting back the lower courses of tributaries, then the heights should be 
accordant in a general sense, unless there is some special reason to the 
contrary. Thus the Stirling Fall and the Lady Bowen Fall, of Milford 
Sound, show some approximation in height, but this is entirely different 
from that of Harrison’s Arm or Sinbad Valley—all reference to elevation 
being made, of course, to the bottom of the sound as the datum-level. 
If these hanging valleys are due to differential erosion, then their preglacial 
form and gradient must have been quite different This general accordance’ 
in height is tacitly admitted by the diagrams used by Davis to illustrate 
his position. He also says (1909, p. 340), “ The depth of glacial erosion 
in the main valley is roughly indicated by the discordant altitude of the - 
hanging lateral valleys, as well as by the height of the main-valley-floor 
steps; but in both cases allowance must be made for the glacial erosion 
of the lateral valleys, or of the bench at the top of the rock-steps.' 
think from this that he evidently would expect all hanging valleys in one 
reach of the main valley to be approximately accordant. 
. Both Gilbert (1904, p. 154, fig. 77) and Garwood (1910, p. 329) certaiuly 
indicate that the floor of hanging valleys in the same main valley are 
occasionally accordant, so that it is possible that the objection made here 
as to the variation in level does not always hold; but if we admit the 
correctness of Russell’s statement cited above, this, too, will result in 
approximate accordance of the lower lips of a suite of hanging valleys of 
approximately the same size. 
[f it be granted that some hanging valleys may be developed from 
corrie basins, then the height of their lips will be dependent on the level 
at which corries can form. Geikie (1902, р. 233) notes that this is related 
to the height of the snow-line, and its level will, in general, be accordant 
under similar conditions of slope and aspect in the same region ; therefore 
the accordance in the level of the floors of corrie glaciers and the hanging 
valleys developed from them is what we might reasonably expect, even 
if they are not to be regarded as due to the overdeepening of the main 
river-valley. The general lowering in height of the corrie-level when fol- 
lowed westward up the valleys of Canterbury is what might be expected, 
since the snow-line falls the nearer approach is made to the main divide. 
It may be noted here that the table given by Penck, and quoted by Geikie 
on page 233 of the work just cited, as to the level at which corrie-lakes 
occur in New Zealand—viz., from 600 to 1,200 metres—gives too restricted 
an upward range, since well-developed cirques and lakes are found at 
heights exceeding 4,500 ft. (1,400 m., approximately). 
Hanging valleys of a typé similar to those occurring in the upper 
Rangitata can be seen in the other valleys of Canterbury—as, for example, . 
on the higher levels on both sides of the Bealey River, in the Waimakariri 
: - between the mouths of the Bealey and Hawdon, also in the Wilberforce 
