FOREST ADVANCE OVER GLACIATED AREAS IN 

 ALASKA AND BRITISH COLUMBIA. 



A very interesting group of facts, involving problems of great 

 import, is embraced in the rate which forests in Alaska and British 

 Columbia have been and are yet following up glacial retreat. 

 The rate of retreat of the one and of the advance of the other are 

 recorded in two ways : ist. By the growth and advance of trees, 

 and 2d, by the increasing depth of forest litter and humus, due to 

 the two, three, or more generations of trees which have grown 

 since the morainic debris, or glaciated surface was left bare by 

 retreating ice. 



After observations upon mountains on which the glaciers were 

 small remnants, the writer visited Alaska for the purpose of study- 

 ing these phenomena where they are best marked in the northern 

 hemisphere. After careful consideration of those glaciers which 

 would give the most reliable types and at the same time would be 

 accessible in the short period available for study Mendenhall 

 Glacier and its former bed were selected for special stud_v. The 

 features herein described for this locality are in general true for 

 immense areas which were observed but not closely studied. It 

 is true that in some instances glacial advance has been recorded 

 by the destruction of young and even full grown forests ; but 

 these instances evidently mark fluctuations in the general glacial 

 retreat which is in progress. After a slight advance the retreat 

 is again taken up, and for a limited period with greater rapidity 

 than marks the retreat of neighboring glaciers. 



Mendenhall Glacier, in Lat. 58° 25' N., Long. 134° 30' \V., 

 occupies the upper portion of a lateral channel jutting off north- 

 easterl}' from the north end of Gastineau Channel. The glacier 

 once occupied the whole of this lateral channel, but has retreated 

 until its face is now some four miles from the junction of the two 

 channels. This lower end is now entirely filled up with glacial 

 debris and overgrown with alder, cotton wood and spruce, with 

 shrubs, mar.sh growth, etc. The lower portion of the filled area 

 is just above tide level ; the upper is about 150 feet above tide 

 level. 



The front of the glacier is some three miles in length and of 

 irregular and varying height ; where long continued melting has 



