374 The American Geologist. june, isos 
hundred feet wider than in 1886. It is evident that when a mass 
so great as that of the Muir glacier is forced through a very narrow 
outlet, the rate of motion through that opening must be ver}' great, 
while any widening of the outlet will largely .decrease the rate. 
D. The form of the ice front of 1886 seems to show that the 
glacier was in an actual state of advance during that season. When 
a glacier, which has both land and water front, remains in a state 
of equilibrium, or of retreat, the water front retreats more rapidly 
than the land front, and forms an eraba3-ment. A projection of the 
water front heyond the land wings indicates positive advance. 
Prof. Reid has set forth wQxy clearl}" the conditions holding at 
the ends of tide-water glaciers. * He shows that the waste by 
melting above the water surface is unimportant, but that the ice in 
contact with the water is melted more rapidly than that exposed to 
the air. Add to this waste the loss by breakage, and it is plain 
that the water front wastes more rapidly than a land front. In 
tide-water glaciers the breakage is the more rapid because of the 
tides, particularly in Glacier ba^-, where the usual tides are about 
fifteen feet and the spring tides as much as twenty -three feet. The 
period of most numerous ice falls in 1886, was the time of spring 
tides. I think Prof. Reid observed the same phenomenon. 
This emba3'ed form is illustrated in most glaciers of to-da}^ 
which have water fronts, as the Greenland glaciers. The Trac}'^ 
glacier of Bowdoin ba}" shows it very plainl}', as pictured by Lieu- 
tenant Pear}-. The Marjelen lake encroached upon the Aletsch 
glacier while it stood at high level. 
But the moraines of the Glacial period show this more plainly, 
since we know that the ice was in retreat or equilibrium while the}^ 
were formed. A great moraine which crosses New Hampshire and 
Vermont turns northward near Burlington and passes through Mil- 
ton, Vt. . to Beekmantown and Altona, N. Y., showing an embay- 
ment of ten to fifteen miles. Mr. Upham writes me: "As 3'ou 
inquire about the glacial lake Agassiz, whether its expanse of 
water washing the ice-front caused it to be indented by an embay- 
ment, as made known by the courses of the terminal moraines 
which come to (and in ver}' low and changed form run aci'oss) the 
lake area, I have to reply, Yes, ver}- definitely so, for the eighth, 
ninth, tenth and eleventh, or respectivel}- the Fergus Falls, Leaf 
Hills, Itasca, and Mesabi moraines. The extent of the indenta- 
*Nat. Geog. Mag., vol. iv, pp. 47-49. 
