CAUSE OF VARIATIONS IO9 
Reid has suggested a local subsidence of the land as 
a possible explanation of the retreat of the glaciers of 
Glacier Bay. 1 Stumps of trees that grew in Muir Inlet 
before the great advance of the glacier, now stand at low- 
tide level, and demonstrate a submergence of at least 
twenty feet. The submergence may have been greater; 
and he points out that any lowering of the surrounding 
land with reference to the sea would make the conditions 
less favorable for the accumulation of snow and tend to 
reduce glaciers. To extend this explanation so as to 
cover the diversity of local histories it would be necessary 
to assume that the Fairweather Range was not lowered 
in company with the adjacent tract about Glacier Bay; 
and it would be logical also to assume that the great ex¬ 
pansion of Glacier Bay ice which preceded its shrinkage 
was associated with a rise of the surrounding land. As 
there is independent ground for believing that the region 
is one of active mountain growth, the occurrence of such 
differential and diverse movements is quite conceivable, 
and their possibility should be kept in view in the study 
of each locality. But as glaciers are highly sensitive to 
climatic changes, as climates are subject to continual and 
rapid variation, and as earth movements are comparatively 
slow and moderate in their influence, the central theory 
of glacier variation is necessarily climatic rather than 
dias trophic. 
With reference to the climatic explanation of the Alaskan 
phenomena I have a suggestion to contribute — a sugges¬ 
tion of a somewhat vague character, not yet reduced to 
the form of a definite hypothesis. It is, that the combi¬ 
nation of a climatic change of a general character with 
local conditions of varied character, may result in local 
glacier variations which are not only unequal but op¬ 
posite. 
J Nat. Geog. Mag., vol. iv, p. 40, 1892. 
