FEBRUARY 16, 1912] 
a former minimum. Having at an earlier 
period been far advanced, and having held 
this position for a long time, the glaciers in 
both regions receded to a stand even far- 
ther back than the present ice fronts, and 
remained there long enough to permit the 
growth of mature forest; then came an 
advance pushing the ice fronts forward 
from 20 to 50 miles. This advance is 
known to have been of brief duration, for 
the gravels over which the glaciers ad- 
vanced were not removed by the ice ero- 
sion; and it was quickly succeeded by the 
rapid recession that has been in progress 
during most of the period of observation. 
So great an advance, followed by so 
ereat a recession, might be expected to be 
part of a general cycle affecting all or a 
large part of the Alaskan field. Yet such 
is not the case, for in Prince William 
Sound, 250 to 300 miles to the west of 
Yakutat Bay, the recent glacier history has 
been wholly different. In no case have the 
glaciers recently had a position far beyond 
their present fronts, while in some eases it 
is certain that they are to-day as far out as 
they have been in a century or two. This 
is especially clearly seen to be the case in 
Columbia Glacier, which in 1909 and 1910 
was advancing into and destroying a ma- 
ture forest. Forest also grows on the 
mountain slopes above the glacier for many 
miles back from its front, suggesting that 
this glacier is now in a state of unusual 
advance analogous to that experienced a 
century or more ago by glaciers to the 
southeast. Since there is no reason to sus- 
pect that a general cause which was op- 
erating to bring about glacier advance in 
the Alaskan coastal region could sufter 
retardation of a full century in the Prince 
William Sound region, we are forced to the 
alternate view that even such great ad- 
vances and recessions as those proved for 
the Yakutat and Glacier Bay regions are 
SCIENCE 
253 
localized phenomena. Whether due to up- 
lift or depression, to vigorous and repeated 
earthquake shakings, or to local climatic 
variations remains yet to be determined. 
Cause of the Recent Retreat of Mur 
Glacier 
It has been a generally favorite theory 
that the remarkable recession of Muir Gla- 
cier since 1899 is an indirect result of the 
great earthquakes of September, 1899. 
Latterly it has been proposed that the re- 
cession is due not to this cause, but to the 
enlargement of ice area exposed to the sea 
water and consequently to wastage by ice- 
berg discharge. Neither of these theories, 
nor the two combined, are either competent “ 
or needed to explain the phenomena of 
recession, though doubtless each has been a 
factor in it. Granting the maximum dis- 
turbance by earthquake shaking, and grant- 
ing even that the glacier could be broken 
from surface to bottom, which is highly 
improbable in view of the nature of ice 
under pressure, the cracks would certainly 
heal and the ice become welded in its 
lower portions soon after the breaking. 
There would be no basis for the continua- 
tion of the effect of the earthquakes for a 
number of years after the shocks them- 
selves had died out; yet recession has con- 
tinued for twelve years after the earth- 
quakes. Moreover, recession began many 
years before the earthquakes, though the 
rate has been much increased since 1899. 
As to the theory that the recession is due 
to the enlarged area of ice exposed to salt 
water, that is surely an efficient aid in 
recession; but it does not account for the 
continuation of notable recession of other 
glaciers in the region which now have less, 
rather than greater, area exposed to the 
salt water. Nor does it account for the 
excessive wastage alone land margins and 
on ice surfaces back from the fronts. 
