ti
and that it was maintained for a considerable period of time. Terraces
were formed running up the Ohio and its tributaries corresponding to the
level that the water must have risen to if the valley were filled up
with ice. These facts, taken with the greater fact that the ice sheet
actually did cross the Ohio Valley into Kentucky, as is shown by the
terminal moraine, seems to prove conclusively the existence of such a
lake during the period that the ice rested at its extreme limit. The
fact that in some places successive terraces are found does not disprove
the theory, because it is more than likely that when the ice receded it
did so in successive stages, remaining at different positions for a
considerable length of time. There is abundant proof of this in the
successive moraines and also in the formation of successive terraces.
Some of these terraces could have been formed from other causes.

It does not require any great stretch of the imagination to understand
how numerous lakes, much larger than any at the present day, may have
extended over large portions of the West and Northwest during the period
that the ice was receding. The ice did not stand with an even thickness
over the surface of the glaciated area, but at some points it moved down
in great lobes, which marked the lines of greatest pressure as well as
the greatest accumulation. As the ice melted away, the thick bodies of
ice might be many, many years in melting, and they might block the
outlet to a very extensive drainage area and thus form a great inland
sea from the vast amounts of water that would come from the melting ice.

All of the region about Winnipeg, in the Red River country, covering
great areas of hundreds of miles in extent, is a level plain only
lacking the coloring to give to one passing through it the effect of a
great unruffled sea. There is no doubt but that all of this region was
the bottom of a great lake at some period when the ice was receding. And
this accounts for the great depth of black soil that we find in this and
other regions. The soil was a water deposit, such as may be found in the
bottom of any shallow lake or pond to-day, and thus many thousand years
ago provision was made for the fertile areas which to-day are feeding
the world with wheat.

We can imagine that during this period the water that flowed off
through the great Mississippi must have been of enormous volume as
compared to the present time. A large portion