Further Exploration of Centre Valley 



the level of a point on the stream in the main valley. 

 The ice, closing the mouth of the tributary valley, had 

 originally stood across the spur at the 830 foot level. 

 The impounded waters had evidently overflowed 

 between the slope of the spur and the side of the 

 glacier, and gradually cut a notch which continued to 

 take the surplus waters until the ice-level had fallen 

 below the level of its intake. It had thus opened a 

 lower outlet which eventually gave rise to the second 

 notch, while a repetition of the same process produced 

 the third and lowest. Streamless valleys of this type we 

 knew to be quite common in the glaciated portions of 

 the British Isles, and we hoped that we might possibly 

 see them in process of formation amongst the glaciers at 

 the head of the valley. 



An investigation of the spur, through which the 

 channels had been cut, showed that it was due to the 

 presence of one of the large dykes of quartz-porphyry, 

 such as we had seen in the valley of the main stream. 



Just above the mouth of the tributary was another 

 moraine, much fresher in appearance than those lower 

 down the valley, and on its northern side was a small 

 lake which had once been much larger, but had been 

 partially filled up by the delta of the stream which issued 

 from a gorge at the foot of the glacier. 



The waters of this stream were milk-white with 

 rock-flour ground from the solid floor and sides of the 

 valley by the friction of the stone-charged ice of the 

 glacier, and bearing eloquent testimony to the enormous 

 erosive power of moving ice. Thousands of tons of this 

 rock-flour must be brought down annually by the waters 

 of this stream alone. The presence of this small lake, 



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