rm, when pastures and
swampy land came under the plough.

Draw a line on the map from New York to St. Louis, and then turn
northward a little and extend it to the Yellowstone Park. The
boulder-strewn states lie north of this line, and are not found south of
it, anywhere. Canada has boulders just like those of our Northern
States. The same power scattered them over all of the vast northern half
of North America and a large part of Europe.

What explanation is there for this extensive distribution of unsorted
debris?

THE QUESTION ANSWERED

The rocks tell their own story, partly, but not wholly. They told just
enough to keep the early geologists guessing; and only very recently has
the guessing come upon the truth.

These things the rocks told:

1. We have come from a distance.

2. We have had our sharp corners worn off.

3. Many of us have deep scratches on our sides.

4. At various places we have been dumped in long ridges, mixed with much
earth.

5. A big boulder is often balanced on another one.

The first thing the geologist noted was the fact that these boulders are
strangers--that is, they are not the native rocks that outcrop on
hillsides and on mountain slopes near where they are found. Far to the
north are beds of rock from which this debris undoubtedly came. Could a
flood have scattered them as they are found? No, for water sorts the
rock debris it deposits, and it rounds and polishes rock fragments,
instead of scratching and grooving them and leaving them angular, as
these are.

Professor Agassiz went to Switzerland and studied the glaciers. He found
unsorted rock fragments where the glacier's nose melted, and let them
fall. They were worn and scratched and grooved, by being frozen into the
ice, and dragged over the rocky bed of the stream. The rocky walls of
the valley were scored by the glacier's tools. Rounded domes of rock
jutted out of the ground, in the paths of the ice streams, just like the
granite outcrop in Central Park in New York, and many others in the
region of scattered boulders.

After long studies in Europe and in North America, Professor Agassiz
declared his belief that a great ice-sheet once covered the northern
half of both countries, rounding the hills, scooping out the valleys and
lake basins, and scattering the boulders, gravel, and clay, as it
gradually melted away.

The belief of Professor Agassiz was not accepted at once, but further
studies prove that he g