THE NORTHERN PACIFIC ROUTE, 
29 
but the map shows that great numbers of them lie on both sides of 
the road. The kettle-like depressions in a moraine, many of which 
FIGURE 3.—Diagram showing isan origin of aliens Kettle holes. A, Bloc 
from a glacier; B, same block after part has 
mud; C, der 
NAT 
ENE 
of ice recently broken 
i melted and the ine poe, with sand and 
are filled with water and become ponds or lakes, are due either to 
irregularities in the deposition of the drift along the front of a glacier 
or to the melting of detached blocks of ice.1 
The map is supposed to represent the 
State as it was when the western ice sheet 
extended southward along the Red River 
valley and deployed to the east into the 
open lands of Minnesota. Part of this 
great glacier found an outlet eastward into 
the upper Mississippi Valley and the val- 
ley of St. Louis River, but the main mass 
of the ice pushed southeastward along the 
valley of Minnesota River. A part over- 
flowed northeastward, forming a lobe that 
covered much of the territory north of St. 
aul. The main lobe swept on south- 
ward across the boundary of the State and 
as far as Des Moines, Iowa. After a time 
the melting at its front exceeded the sup- 
ply of fresh ice coming from the teens 
and then the glacial in began 
retreat, and teeta the ice disap’ 
When the ice 2 the Superior sheet 
melted back into that basin the ponding 
of water between the ice front and the 
formed between the front of the elect 
oe Se north and the 
Browns Valley 
Over sini aii ae tie eatin ans 
drift of Minnesota there has been little 
change since the ice disappeared except 
the formation of soil and a slight leaching 
and weathering; but in some places nota- 
ble changes have 
of Minnesota’s 
show beaches at higher levels than the 
present, their outlets having been cut 
down by the water at various stages. 
Many lakes have been so filled with sedi- 
ment as to become marshes or even dry 
land, and many have been filled by the 
growth of peat. St. Anthony Falls, on 
the Mississippi, has retreated a few feet a 
year until recently checked by an arti- 
ficial retaining wall. Minnehaha Falls, 
mi stream erosion since the last 
glaciation is slight, and on many 
it is scarcely enough to be measurable. 
1 When a glacier reaches its greatest 
extension and begins to retreat, its pause 
and recession mean that the supply of 
fresh ice or snow back at the gathering 
ee where. it receives most of its mate- 
prin that goes on over - its entire sur- 
face, but more particularly at its outer 
. The result is that the ice near 
the extremity moves forward very slowly 
and finally ceases to move at all. The 
edge of the ice sheet becomes thin and 
, and, owing to more rapid 
melting along cracks or crevasses, 
of ice become separated from the main 
B 
Pek ech 4: ok as shown at A in 
figure 3, above, may be uncovered, but 
