regular, shooting out into
curves and then receding. This line of extreme ice flow is marked by
glacial drift so prominently that no one who has studied glacial action
can doubt for a moment what was the cause of these deposits. The line
is called the "terminal moraine." By examining a map of North America
and tracing the line of the moraine as we have described it, it will be
seen that about two-thirds of North America was at one time covered with
ice to a greater or less depth. How deep, is simply a matter of
conjecture, but in the central portions of the great glacier, where was
the bulk of snowfall, it must have reached a depth of several miles to
account for the enormous pressure that would be required to carry the
ice so far southward.

But let us go back and define what is meant by a moraine. A moraine is a
name given to the deposits that are of stone, gravel, and earth that
have been carried along by the movement of the glaciers and deposited at
their margins, sometimes piled up to great depths. The composition of
these moraines is determined of course by the nature of the country over
which the stream of ice is flowing. Bowlders of enormous size have been
carried for hundreds of miles, and the experienced geologist is able to
examine any one of them and tell us where its home was before the
glacial period. Moraines are divided into different classes according to
their position and constitution. The moraine found at the extreme limit
of ice-flow is called the "terminal" moraine, as before mentioned. Those
that are found inside of this line and between two flows are called
"medial" moraines. There is a subdivision called "kettle" or "gravel"
moraines, which are very prominent in northern Illinois and southern
Wisconsin, and may be said to culminate in the vicinity of Madison. This
moraine is a great deposit of gravelly soil. Where this moraine exists
the face of the country is covered with "kettle holes" of all sizes and
shapes, and in some of them there are small lakes, while others are dry.
The great chain of inland lakes that are found in southern Wisconsin and
northern Illinois were formed by deposits of ice that had been covered
by glacial drift, gravel and otherwise, brought down and deposited upon
these masses of ice which gradually melted away, leaving a depression at
the points where they lay, while the drift that was piled around them
loomed up and became the shores of the lake. This is substantially Dr.