Wright's theory, who studied the formation of these "kettle holes" at
the mouth of the Muir glacier. This enthusiastic glacialist has spent
many summers tracing the terminal moraine with its fringe along the
lines heretofore indicated. He is, therefore, entitled to speak with
authority on matters of glacial action.

The part of the country that has been plowed over by these glaciers is
called the glaciated area and the rest the unglaciated. The whole of
North America north of the line of the terminal moraine that we have
traced is a glacial region, with the exception of a few hundred square
miles chiefly in Wisconsin, where the ice seemed to have parted and
passed around this area, coming together again on the south side of it.
The ice probably did not reach the extreme limit that shows glacial
deposit, but undoubtedly the effects of it are seen for some distance to
the south, owing to the fact that during the time it was melting great
quantities of water flowed away from the extreme edge of the ice,
carrying with it more or less of the glacial drift, which was deposited
for some distance to the south. When the ice receded it undoubtedly
paused at different points, where it remained stationary for a long
period of time. I mean stationary at its edges, for the flow of ice was
continually moving, but in its progress southward it came to a point
where the heat was sufficient to melt the ice as fast as it arrived at
that point. The on-moving ice was continually bringing with it the
debris that it had gathered up at different points on its journey, so
that it is easy to see how these moraines could accumulate to a greater
or less depth at the margin of the ice flow, which would be determined
by the duration of the period it remained stationary. This, however, is
only one factor, as the surface of the earth in some parts of the
country would be more easily picked up and carried than in others;
therefore, the drift accumulated much more rapidly in some sections than
in others.

Another factor that was active in the more rapid accumulation at certain
points was the speed at which the ice moved, and this would be
determined by the pressure that was behind it, and there would always be
lines of unequal pressure existing in such a great glacier as must have
existed when these moraines were formed.

As an instance of the difference in the glacial deposits that are made
in different periods during the time of the melting of the