SpricHt.—Hanging Valleys of the Upper Rangitata Valley. 97 
Valley. It cannot be urged that these have been formed by sapping-back 
along lines of structural weakness, since some of them lie across those lines, 
but the method of formation is analogous to those in the Havelock. Some 
of them certainly show a tendency to enlarge their heads along the strike 
when their general direction crosses it at right angles. 
Although it is here urged that many of the hanging valleys of the alpine 
area of Canterbury are not to be attributed directly to differential erosion, 
there are some cases which may be explained in that way. Andrews Creek, 
a tributary of the Waimakariri on the north side, between the junctions 
of the Hawdon and Poulter, may be attributed to this cause, since there 
is good evidence of overdeepening in this portion of the Waimakariri Valley : 
but the possibility of the discordance being due to tectonic movements 
in this case must not be overlooked, though I do not think it probable. 
There are тфу a however, which need special consideration. The 
formation of Arthur’s Pass is most easily explained by supposing that it 
is due to two hanging valleys which have sapped back along the strike of 
the beds, one from the west-coast side and the other from the Bealey side 
of the range, and the drainage has ultimately been captured by the former, 
leaving both ends of the valley in a hanging condition. An exactly 
analogous case occurs in Browning Pass—not the well-known pass at the 
head of the Wilberforce, but one which leads from the valley of the White 
River, one of the feeders of the Waimakariri. Another type of hanging 
Walker’s Pass, at the head of the Hawdon; and again on the western side 
of the upper Waimakariri River to the south of Mount Айыб. Опе 
description applies i in all these cases. 
The main stream comes from a northerly direction parallel to the strike 
of the beds, and flows along the floor of a characteristic deep glacial 
trough. The walls, notably the western, are precipitous, and streams 
сае cascade over them from hanging-valley mouths. The floors of 
these hanging vallevs cut across the strike, but they have been reduced 
to such an extent that they furnish fairly easy т across the main 
divide to the valleys of the western slope, and the streams occupying them 
are partially or wholly diverted to the west, as in the case of Brownin 
Pass 
The marked discordance in these cases is to be attributed to the facility 
with which stream and glacier erosion has proceeded along the strike, so 
that overdeepening has taken place in these cases, whereas erosion across 
the strike has been slow. The erosion of the main valley was in all 
probability due to stream-action initially, but serious modification of the 
valley has followed, and foe present landscape-features are those attributable 
to ice-action rather t n to stream-action. It is conceivable, how ever, 
that stream erosion oan ойны a steep-sided valley in these cases, since 
the beds dip at high angles and hard bands occurring at regular intervals 
in the greywacke series help to maintain that approach to perpendicularity 
which was impressed on the valley-walls by ice-action. 
At various places in the above discussion I have suggested that the 
modification of the valleys of the Southern Alps by glaciation has hardly 
been of the profound order originally indicated by Hector and Haast, and 
endorsed by later кесюш, including myself. My reasons for doubting 
the statement are— 
(1.) The general absence of discordance in the grade of the tributaries 
at the point of junction with the main streams. 
4— Trans. 
