102 ALASKA GLACIERS 



has not very greatly exceeded its present size. During 

 that period it may or may not have been much smaller 

 than now. (2) During the latter part of that period the 

 glacier advanced to the forest line and then retreated. 

 This maximum probably occurred as much as fifty years 

 ago to allow for the disappearance of the overturned 

 trees but could hardly have been so early as the begin- 

 ning of the nineteenth century, else there would be larger 

 spruces below the forest line. (3) Several decades ago 

 there was a maximum, affecting especially the central part 

 of the glacier, and retreat from this was still in progress 

 to the close of the century. 



There was little difference in the extent of the two 

 maxima, and although their separateness was not doubted 

 during my visit, it now seems to me possible that the two 

 were identical. One was inferred wholly from the fea- 

 tures of the valley wall, and the other wholly from the 

 frontal moraine. The straggling of young spruces below 

 the forest line afforded so strong a contrast to the absolute 

 barrenness of the morainic mounds that the possibility of 

 connecting the two groups of phenomena with the same 

 event did not occur to me; but DalPs observation of ice 

 remnants in the moraine in 1880 suggests a local cause 

 for the sterility of the gravel mounds and leaves the 

 matter in doubt. 



SUMMARY OF MODERN CHANGES 



During the last twenty years much attention has been 

 given to the variations of glaciers, and a large body of 

 facts has been collected, especially with reference to 

 European examples. In attempts to generalize these 

 facts serious difficulties have been encountered, and their 

 discussion has not yet resulted in a satisfactory theory of 

 the causes of change. All students of the subject feel the 

 need of more extended observation, and from the point of 



