332 Transactions. 



mountains, due to an elevation of the land, rendering larger areas subject 

 to the action of heavy frost, which is the chief agent of denudation on moun- 

 tain areas. The same effect may be produced by supposing the climate to 

 have been slightly more rigorous than that existing at present. In a former 

 paper on the " Terrace-development in the Valleys of the Canterbury 

 Kivers " I have already noted as a deduction from the condition of shingle 

 fans, and from peculiarities in the form of the river-beds, that there has 

 been a falling-oli in the supply of waste, and this observation on the moraines 

 tends in the same direction. In the paper referred to, I attributed this 

 falling-off to a lowering of the land, just as I attributed the severer glacia- 

 tion to elevation of the land. My present opinion is by no means decided 

 that this was the predominating cause. Elevation certainly occurred, and 

 this would assist other causes tending in the same direction, such as a modi- 

 fication of the climate. Whether the retreat of the glaciers has been due 

 to a lowering of the land or to an amelioration of the climate, the supply 

 of waste has fallen off, as well as the supply of snow, which determines the 

 existence of the glaciers. If the former falls off in a higher ratio, then there 

 will be no moraines ; if, -however, the waste increases in a higher ratio than 

 that of the transporting-poM^er of the streams resulting from the melting 

 of the snow, moraines will certainly form. This will occur in general when 

 there is a temporary advance of the ice due to climatic or other causes, 

 just as failure to form moraines will occur during retreat. The frequent 

 absence of moraines from the front of Pleistocene ice-sheets may perhaps be 

 explained by the amount of water formed at their terminals being in excess 

 — probably much in excess — of that necessary to transport the relatively 

 small amount of material which usually accumulates on the surface of the 

 ice-sheet and beneath it. 



6. Former Glaciatiox. 

 {a.) General. 



It may be inferred from the statements made previously in this article 

 that in former times the country was subjected to a more severe glaciation. 

 The proofs of the former extension of the ice are found on every hand. 

 These may be summarized as follows : Old moraines, roches moutonnees, 

 striated surfaces, ice-shorn and ice-terraced slopes, valleys with charac- 

 teristic U section with truncated and semi-truncated spurs, and spui's with 

 triangular facets. A deposit of boulder-clay with large angular fragments 

 is found at the Potts River, where, according to Haast, there are the most 

 characteristic subglacial deposits to be found in New Zealand. I do not 

 know of any discovery recorded later which necessitates a revision of this 

 statement. 



The limits of this glaciation to the eastward were in all probability not 

 beyond the line of the foothills flanking the eastern moimtains. Glaciers 

 certainly came through the Ashburton Gorge down to the neighbourhood 

 of the Mount Somers Township, since immediately behind it there is a 

 terrace formed of washed material containing large angular blocks which 

 look like those deposited in streams at the immediate front of a glacier. 

 The smoothed and rounded hills in the locality are also suggestive of ice- 

 action. But the occurrence of lateral moraines high up on the hills flanking 

 the gorge on the south is conclusive proof of its presence, and shows that 

 even in that part of the country there was very great thickness of ice at 

 the maximum glaciation. On the northern side of Mount Hutt, glaciers 



