Further Exploration of Centre Valley 



roughly parallel to the sides of the valley, but slightly 

 inclined outwards like the ribs of a fan. As we left the 

 termination behind, these longitudinal crevasses became 

 fewer and fewer, until when we arrived on the top of 

 the slope they had entirely disappeared. 



We had now before us a wide spread of rough ice 

 with many scattered blocks of gneiss and granite and 

 numerous long ridges of stones and rubbish upon its 

 surfaces. Away in the distance the ridges of rubbish 

 " rock-trains" as they are often called appeared to 

 coalesce, so that, in place of the twenty or thirty which 

 were present near the termination, there were but four, 

 but these were much larger. 



The small rock-trains appeared to have been formed 

 by the subdivision of the larger ones, and we determined 

 to find out if this were the case, and, if so, how it came 

 about ; we therefore walked some distance towards the 

 head of the glacier. 



Some of the larger rock-trains stood 30 feet above 

 the general surface, and appeared, at first sight, to 

 consist entirely of stones and sand. Careful examina- 

 tion of one of them revealed the fact that it consisted for 

 the most part of a ridge of ice with a comparatively thin 

 coating of rock debris on its surface. 



The effect of sand and stones upon the rate of 

 melting of the surface depends upon the size of the 

 stones and the thickness of the layer. Let us first 

 consider the case of detached stones. The direct rays 

 of the sun have little melting effect upon the ice, as the 

 greater part of the heat is reflected from its surface. 

 Stones, however, absorb the heat, and soon themselves 

 become heated, and the same is true of the sand and fine 



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