Marshall. — The Glaciation of yeiv Zealand. 339 



this term is almost restricted to the amphitheatre at the head of a glacial 

 valley. The Arrow basin is at the junction of at least two glacial valleys 

 of considerable length. 



The lateral thrust of the Greenstone Glacier is a difficult matter to 

 understand.* The fact that the Greenstone River flows for five miles of its 

 course through a profound narrow gorge before it joins the Caples appears 

 to be a sufficient proof that the ice of the Greenstone Glacier never passed 

 into the Wakatipu basin. Such a conclusion is strongly supported when 

 it is recognised that the upper Greenstone Valley has a direct continuation 

 to the Mararoa over a pass formed of stratified gravels only a few hundred 

 feet high. Large moraines exist at the lower end of the Mavora Lake. 

 The ice from the Caples imdoubtedly joined the Lake Wakatipu Glacier 

 and deposited morainic matter at Rere Lake, but it did not join it at right 

 angles, and cannot have exerted the thrust which is stated to have produced 

 such important effects on the opposite slopes of the Richardson Mountains. 

 Such a thrust is hard to understand, for it is known that the ultimate 

 strength of ice is so small that it would be reduced to the physical state 

 of a fluid long before the pressure was sufficient to bend or break the least- 

 resistant schist. The described effect of the Von Glacier is equally difficult 

 to follow, for there is a low pass from this valley to the Oreti, and it is 

 certain that the Wakatipu ice, if it reached the thickness, would have flowed 

 over into the Oreti, for it is stated that it " strode over " Mount Nicholas, 

 which is 4,827 ft. above sea-level. There was certainly no opposing mass 

 of ice of great magnitude to prevent an overflow into the Oreti Valley. 



At the present time it is rash to make ass rtions as to the source of the 

 boulders found in moraines, for nothing is at present known of the structure 

 of the country at the head of the Dart or even of the Shotover. Li the case 

 of the former, at least, it is quite possible that gabbros and other plutonics 

 may exist, for they are known on the western side quite close to the water- 

 shed. It is still more likely that greywacke rocks may yet be found in 

 many localities within the Dart watershed. 



The actual thickness of the ice is stated to have been 7,490 ft. near the 

 Kingston end of Lake Wakatipu. Judging from analogy with the surface 

 of the Greenland ice-sheet, the slope of the upper surface of the Wakatipu 

 Glacier, even if it is regarded as an ice-sheet, cannot have been less than 

 90 ft. per mile to the west of this point. Mount Crichton is about twenty- 

 five miles away from it in the direction of the flow of the ice, and the 

 surface of the ice there would be 2,250 ft. higher. Li other words, the 

 ice-surface would be 9,950 ft. above sea-level. As Mount Crichton is only 

 6,185 ft. high, the ice would have been 3,765 ft. above its summit. To 

 any one who has ascended the hills around Lake Wakatipu it is evident 

 that ice has never flowed over their tops. One of the first effects of the 

 movement of an ice covering is to remove all loose blocks and boulders ; 

 but when it melts it will leave behind a few foreign boulders which it has 

 carried with it from elsewhere. The photograph on page 80, f of Mount 

 Aurum, which is 7,315 ft. high, shows that it has not been covered by a 

 moving sheet of ice. Every tourist knows of the litter of loose blocks on 

 the summit of Ben Lomond, which is 5,967 ft. high. I have found 

 the same thing on the top of the Livingstone Mountains, and on that of 

 Mount Dick, 6,021 ft., which rises above the point where Lake Wakatipu 



* Bulletin No. 7, N.Z. Geological Survey (New Series), p. 31. f Loc. cit, p. 80. 



