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 Dali’s 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 
