does not differ materially from its effect
all over southern Canada and the northern United States from New England
to Kansas and Minnesota. Each year the people of these regions are
richer by perhaps a billion dollars because the ice scraped its way down
from Laurentia and spread out over the borders of the great plains on
the west and of the Appalachian region on the east.

We have considered the Laurentian highland and the glaciation which
centered there. Let us now turn to another highland only the northern
part of which was glaciated. The Appalachian highland, the second great
division of North America, consists of three parallel bands which extend
southwestward from Newfoundland and the St. Lawrence River to Georgia
and Alabama. The eastern and most important band consists of hills and
mountains of ancient crystalline rocks, somewhat resembling those of the
Laurentian highland but by no means so old. West of this comes a broad
valley eroded for the most part in the softer portions of a highly
folded series of sedimentary rocks which are of great age but younger
than the crystalline rocks to the east. The third band is the Alleghany
plateau, composed of almost horizontal rocks which lie so high and have
been so deeply dissected that they are often called mountains.

The three Appalachian bands by no means preserve a uniform character
throughout their entire length. The eastern crystalline band has its
chief development in the northeast. There it comprises the whole of New
England and a large part of the maritime provinces of Canada as well as
Newfoundland. Its broad development in New England causes that region to
be one of the most clearly defined natural units of the United States.
Ancient igneous rocks such as granite lie intricately mingled with old
and highly metamorphosed sediments. Since some of the rocks are hard and
others soft and since all have been exposed to extremely long erosion,
the topography of New England consists typically of irregular masses
of rounded hills free from precipices. Here and there hard masses of
unusually resistant rock stand up as isolated rounded heights, like
Mount Katahdin in Maine. They are known as "monadnocks" from the
mountain of that name in southern New Hampshire. In other places larger
and more irregular masses of hard rock form mountain groups like the
White Mountains, the Green Mountains, and the Berkshires, each of which
is merely a great series of monadnocks.

In