JDin- Glac/ii' RiKjloii^ Alaxl-a. — Cu-shlng. 223 
microscopicall}- b}' Dr. F. H. Heiiick of Adelbert College and 
compared with sections of the more common spruce now growing 
on the Alaskan mountains, and he pronounces them almost cer- 
tainl}' identical. 
Destruction of the Forest. — The trees were removed from this 
region by a recent advance and increase in size of the various 
glaciers in the vicinity'. Those on the low grounds were partially 
preserved in position by the thickness of soft deposits laid down over 
them. The old trees appearing on the tops of the mountain ridges 
ten miles down the bay, mark the point l)eyond which the ice 
ceased to cover the tops of these ridges at its period of greatest 
extent, or at least the point where permanent snow fields ceased, if 
the main ice stream did not reach this hight. 
The hearing of this forest on the history of Muir glacier. — South- 
ern Alaska has all been glaciated. Since the retreat of the gla- 
ciers from most of the valleys their slopes have become densely 
clothed with timber. The evidence just presented seems to neces- 
sitate the conclusion that Muir glacier retreated much bej'ond its 
l^resent position, and remained in that dwarfed condition at least 
sufflcientl}' long to permit the growth of a multitude of great trees 
upon the mountains around Glacier bay and Muir glacier amphi- 
theatre. Then the glacier advanced and destroyed these trees. In 
this advance it extended down the bay nearlj' to the Beardslee is- 
lands, and in Mine inlet had a thickness at least 2,000 feet greater 
than at present. From this last advance it is now rapidly retreat- 
ing. The fresh condition of the old wood, its abundance on the 
mountains in protected spots, and the distribution of living trees 
in the lower Glacier V)ay region, all combine to render it impossi- 
l)le to adopt Prof. Wright's suggestion that this old forest was 
pre-glacial. in the sense in which he uses it.* It is rather inter- 
glaciah and comparatively recent. Muir glacier has not steadily 
retreated since the great Cordilleran glacier began to vanish, but 
is now retreating from a comparatively slight advance which fol 
lowed upon the heels i)i a great and somewhat prolonged reces- 
sion. Already young spruces are beginning to shoot up here and 
there upon the timl^erless mountains, and it cannot be a matter 
of many centuries before tiiey will again resume the characteristic 
Alaskan forest covering. Further evidence of the truth of this 
view is furnished by a little coral, one of several found attaoluMl 
• *Ice Age in North America. 
