MUIR GLACIER 23 



was only 1,900 feet. It is therefore probable that the 

 summer rate of retreat is much more rapid than the winter. 



While these considerations tend to qualify the figures 

 deduced from uncorrected observations, they do not affect 

 their general tenor. The application of a correction 

 for seasonal oscillation would diminish by a few hun- 

 dred feet the estimate for the total retreat from 1886 to 

 1890, and increase by a similar amount the estimate for 

 the total retreat from 1892 to 1899, but would leave un- 

 changed the general result that the retreat in nineteen years 

 has been more than a mile and a half, and that the general 

 retreat suffered at least one interruption, a small advance 

 occurring between 1890 and 1892. 



The general change of contour mentioned above is of 

 peculiar interest because it was predicted by Reid. The 

 middle of the glacier ends in deep water, a maximum 

 sounding of 720 feet having been recorded, but at each 

 side of the rock trough the ice rests on a bank of gravel 

 rising above the water level. Observing that the surfaces 

 of these gravel banks descend northward beneath the 

 glacier, Reid inferred that with the progress of recession 

 lanes of sea water would soon be admitted between the 

 ice and the gravel; and having determined that the mar- 

 ginal parts of the glacier advance very slowly as compared 

 to the medial, he inferred that their cliffs would be carried 

 back with relative rapidity by the attack of the warm sea 

 water. As the map shows, these expectations have been 

 fully realized. 



In bringing the record of the glacier down to the sum- 

 mer of 1899 the preceding paragraphs practically close a 

 division of its modern history, for a new epoch was intro- 

 duced only three months after our visit. On the I2th of 

 September the southern coast of Alaska was shaken by a 

 severe earthquake, and other shocks followed at intervals. 

 These greatly modified the condition of its tidal glaciers, 



