94 Transactions. 
The explanation which credits the formation of hanging valleys to 
deepening by rivers while the tributaries are protected by ice also fails, 
since there is almost entire absence of evidence of deepening, but strong 
evidence in favour of aggradation. In no case that І am aware of, where 
a glacier at present reaches the level of the valley-floor, is the stream 
deepening its bed in front of the glacier-face ; in every case the stream is 
overloaded with sediment, and is aggrading rather than eroding its bed. 
These two hypotheses, therefore, do not afford a satisfactory solution 
of the problem as far as hanging valleys in the region under consideration 
are concerned. The suggestion made by the present author is that 
hanging valleys are at times due to progressive head-erosion of the rocks 
along belts of structural or lithological weakness. 
The hanging valleys in the Havelock district are certainly associated 
with such belts, and have been eroded principally along the strike of the 
beds. This is clearly seen in that valley whose head is in the vicinity of 
Cloudy Peak (Plate 8, fig. 1). Cup-shaped hollows in an earler stage 
here, then the typical form would be developed ; and if the mouth or lip 
over which the water falls into the main valley were marked by the 
the tributary glacier, or from the tributary valley after ice had dis- 
appeared, established itself on an easily eroded bed, then the floor would 
rapidly be adjusted to the main valley. 
ese small valleys with grades adjusted posterior to the glaciation 
are entirely distinct in origin from the main tributaries whose valleys were 
formed in preglacial times, and which have maintained their accordance. 
ensues is a kind of double-headed valley. In the incipient hollows along- 
side these typical valleys, and grading into them, as regards their main 
features the same process is to be seen, but the result is not yet 80 
pronounced. The lengthened member of the double-headed trough often 
forms a pass between adjacent and parallel main valleys. 
The fact that so many of the hanging valleys have been eroded on the 
strike of the beds results chiefly from the fact that the main river direc- 
tions were initially determined across it. Thus the remarkable and regular 
series on the west bank of the Clyde are arranged at right angles to the 
Clyde for this reason; but where the strike-direction varies locally, and 
also in the higher reaches of the rivers where the tendency of the main 
stream is to set itself parallel to the strike, the hanging valleys across the 
strike are increasingly numerous. 
| If such valleys arise from the development of glacier-filled hollows 
the level of the lip will be controlled initially by the height at which 
