e large amount of quartz in the rocks. That would be a
small handicap, however, provided the soil were scores of feet deep like
the red soil of the corresponding highland in the Guiana region of
South America. But today the North American Laurentia has no soil worth
mentioning. For some reason not yet understood this was the part
of America where snow accumulated most deeply and where the largest
glaciers were formed during the last great glacial period. Not once but
many times its granite surface was shrouded for tens of thousands of
years in ice a mile or more thick. As the ice spread outward in almost
every direction, it scraped away the soil and gouged innumerable hollows
in the softer parts of the underlying rock. It left the Laurentian
highland a land of rocky ribs rising between clear lakes that fill the
hollows. The lakes are drained by rapid rivers which wind this way
and that in hopeless confusion as they strive to move seaward over the
strangely uneven surface left by the ice. Such a land is good for the
hunter and trapper. It is also good for the summer pleasure-seeker who
would fain grow strong by paddling a canoe. For the man who would make
a permanent home it is a rough, inscrutable region where one has need of
more than most men's share of courage and persistence. Not only did
the climate of the past cause the ice to scrape away the soil, but
the climate of the present is so cold that even where new soil has
accumulated the farmer can scarcely make a living.

Around the borders of the Laurentian highland the ice accomplished a
work quite different from the devastation of the interior. One of its
chief activities was the scouring of a series of vast hollows which
now hold the world's largest series of lakes. Even the lakes of Central
Africa cannot compare with our own Great Lakes and the other smaller
lakes which belong to the same series. These additional lakes begin
in the far north with Great Bear Lake and continue through Great Slave
Lake, Lake Athabasca, and Lake Winnipeg to the Lake of the Woods, which
drains into Lake Superior. All these lakes lie on the edge of the great
Laurentian shield, where the ice, crowding down from the highland to
the north and east, was compressed into certain already existent hollows
which it widened, deepened, and left as vast bowls ready to be filled
with lakes.

South and southwest of the Laurentian highland the great ice sheet
proved beneficial to man. There, instea