untains furnish.

Thus it will be seen that the progression and recession of the ice have
not only formed great lakes, changed river beds, and covered a million
square miles of area with glacial drift averaging fifty feet in depth,
making many waterfalls and giving variety to the surface of the earth,
besides producing the finest agricultural region in the world, but have
also given variety to our forests and plants wherever this ice sheet has
extended.

CHAPTER XXIX.

DRAINAGE BEFORE THE ICE AGE.

We have already said that during the ice age river-beds were changed,
valleys were filled up, new lakes were made, and waterfalls created.
Great as were the changes made by the carrying power of moving ice,
still greater were those made in preglacial times; not, however, from
the action of moving ice, but from running water. Erosion caused by
running water has, probably, during the life of the world, transported
more material from place to place, from mountain to valley, and from
valley to ocean, than any other agency; chiefly for the reason that it
has been so much longer doing its work.

The valley of the Ohio River, a thousand miles or more in length,
together with the great number of feeders that empty into it, is an
instance of the wonderful erosive power of running water. The valley of
the Ohio River will probably average a mile in width at its upper level
and, deep as it is to-day, it was much deeper in preglacial times. There
is evidence that the whole bed of the river was from 100 to 150 feet
deeper than it is at present. This has been determined by borings at
different points to ascertain the depth of the drift that was lodged
during the glacial period in the trough of the Ohio River. Anyone
traveling up or down the river to-day can readily see that it is a great
sinuous groove cut down through the earth by millions of years of water
erosion, and not only this, but that at some time in its history this
great valley has been partly filled, forming on one or both sides of the
river level areas--called bottom land. These lands are exceedingly
productive, owing to the great depth and richness of the soil.

For many years the writer lived upon one of the rivers tributary to the
Ohio and often made trips by steamboat up and down the Ohio River.
Traveling along this river a close observer will be struck by the
exactness of the stratifications in the rock and in the coal beds to be
seen on each side of the ri