34 THE MOUNTAINS OF CALIFORNIA 



ting clear sections through the porous surface-ice 

 into the solid blue, where the structure of the glacier 

 was beautifully illustrated. 



The series of small terminal moraines which I had 

 observed in the morning, along the south wall of the 

 amphitheater, correspond in every way with the 

 moraine of this glacier, and their distribution with 

 reference to shadows was now understood. When 

 the climatic changes came on that caused the melt 

 ing and retreat of the main glacier that filled the 

 amphitheater, a series of residual glaciers were left 

 in the cliff shadows, under the protection of which 

 they lingered, until they formed the moraines we 

 are studying. Then, as the snow became still less 

 abundant, all of them vanished in succession, except 

 the one just described ; and the cause of its longer 

 life is sufficiently apparent in the greater area of 

 snow-basin it drains, and its more perfect protection 

 from wasting sunshine. How much longer this little 

 glacier will last depends, of course, on the amount 

 of snow it receives from year to year, as compared 

 with melting waste. 



After this discovery, I made excursions over all 

 the High Sierra, pushing my explorations summer 

 after summer, and discovered that what at first 

 sight in the distance looked like extensive snow- 

 fields, were in great part glaciers, busily at work 

 completing the sculpture of the summit-peaks so 

 grandly blocked out by their giant predecessors. 



On August 21, I set a series of stakes in the 

 Maclure Glacier, near Mount Lyell, and found its 

 rate of motion to be little more than an inch a day 

 in the middle, showing a great contrast to the Muir 



