456 PROCEEDINGS OP SECTION C, 



U-sliaped valleys in Southern New Zealand, or elsewhere, may be 

 formed in the following ways : — 



(1) By glacier excavation along a pre-existing stream valley. 



(2) By glacier excavation along a fault line. 



(3) By trough faulting, the effects of which may be enhanced by 

 ice corrasion. 



" Glacial valleys may originate by ice corrasion alone, but in the 

 southern part of New Zealand their formation has been much aided 

 by zones of crushed rock fault-produced. In some cases block or 

 trough faulting is largely, perhaps even mainly, responsible for U-shaped 

 valleys, which have at one time been occupied by glaciers." 



Reference is made in the paper to the small rock-bound basins or 

 flats which are common among the Weatland mountains. These are 

 considered to be excavated sometimes by ice action alone, but more 

 commonly the glacier has been aided by the existence of a body of 

 crushed rock — fault-produced — at the points where these flats occur. 

 Some may be due to trough or block faulting. 



The larger and deeper rock-bound basins, occupied as a rule by 

 lakes, are stated to be due to trough-faulting. Some " glacial " lakes, 

 however, if of moderate size and depth, may be produced by ice excava- 

 tion alone, especially at or below the junction of two ice streams. 

 Others are formed by the damming up of a glacial valley by terminal 

 moraine, and some lakes are increased in depth by the same cause. 



When a glacial lake has originated in trough-faulting it is believed 

 that the faulting went on during the time of the glacial extension, so 

 that the depression filled with ice as it formed. This ice is supposed 

 to have remained almost quiescent, whilst the upper part of the glacier 

 was in more or less active movement, over-riding the lower portion 

 below the level of the rock rim, or in some instances below the terminal 

 moraine. On the retreat of the glacier the melting of the ice left a 

 hollow — the basin of the modern lake. 



"If the views herein advanced be substantially correct, it is evident 

 that the glacial lakes and valleys of Southern New Zealand are ac- 

 counted for without recourse to the theory of a glacial" epoch, or an 

 extraordinary increase in the size of the present glaciers." 



U.— ON THE LOWER CAMBRIAN AGE OF THE BARRIER 

 RANGE (NEW SOUTH WALES), PREVIOUSLY RE- 

 GARDED AS SILURIAN (?). 



By D. MAW SON, B.E., B.Sc. 



