CAUSE OF VARIATIONS 109 



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 

 diastrophic. 



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. 



*Nat. Geog. Mag., vol. iv, p. 40, 1892. 



