sheer and
unimaginable force with which the floes are driven against the edge of
the glacial fringe, just as farther out the pressure ridges are caused
by the force with which the great floes themselves are crushed and
smashed together by the force of the wind and the tides.

These pressure ridges may be anywhere from a few feet to a few rods in
height; they may be anywhere from a few rods to a quarter of a mile in
width; the individual masses of ice of which they are composed may vary,
respectively, from the size of a billiard ball to the size of a small
house.

Going over these pressure ridges one must pick his trail as best he can,
often hacking his way with pickaxes, encouraging the dogs by whip and
voice to follow the leader, lifting the five-hundred-pound loaded
sledges over hummocks and up acclivities whose difficulties sometimes
seem likely to tear the muscles from one's shoulder-blades.

Between the pressure ridges are the old floes, more or less level. These
floes, contrary to wide-spread and erroneous ideas, are not formed by
direct freezing of the water of the Arctic Ocean. They are made up of
great sheets of ice broken off from the glacial fringe of Grant Land and
Greenland, and regions to the westward, which have drifted out into the
polar sea. These fields of ice are anywhere from less than twenty to
more than one hundred feet in thickness, and they are of all shapes and
sizes. As a result of the constant movement of the ice during the brief
summer, when great fields are detached from the glaciers and are driven
hither and thither under the impulse of the wind and the
tides--impinging against one another, splitting in two from the violence
of contact with other large fields, crushing up the thinner ice between
them, having their edges shattered and piled up into pressure
ridges--the surface of the polar sea during the winter may be one of
almost unimaginable unevenness and roughness.

At least nine-tenths of the surface of the polar sea between Cape
Columbia and the Pole is made up of these floes. The other one-tenth,
the ice between the floes, is formed by the direct freezing of the sea
water each autumn and winter. This ice never exceeds eight or ten feet
in thickness.

The weather conditions of the fall determine to a great extent the
character of the ice surface of the polar sea during the following
winter. If there have been continuous shoreward winds at the time when
the increasing cold was g