e sand. It is impossible to
think that the ocean has subsided. The only explanation that accounts
for the ancient beach, high and dry on the side of Greenland's icy
mountain is that the continent has been lifted a thousand feet above its
former level. This is an accepted fact.

We know that climate changes with changed altitude as well as latitude.
Going up the side of a mountain, even in tropical regions, we may reach
the snow-line in the middle of summer. Magnolia trees and tree ferns
once grew luxuriantly in Greenland forests. Their fossil remains have
been found in the rocks. This was long before the continent was lifted
into the altitude of ice and snow. And it is believed that the climate
of northern latitudes has become more severe than formerly from other
causes. It is possible that the earth's orbit has gradually changed in
form and position.

If Greenland should ever subside until the ancient beach rests again at
sea-level, the secrets of that unknown land would be revealed by the
melting of the glacial sheet that overspreads it. Possibly it would turn
out to be a mere flock of islands. We can only guess. North America had,
not so long ago, two-thirds of its area covered with an ice-sheet like
that of Greenland, and a climate as cold as Greenland's. At this time
the land was lifted two to three thousand feet higher than its present
level. All of the rain fell as snow, and the ice accumulated and became
thicker year by year. Instead of glaciers filling the gorges, a great
ice flood covered all the land, and pushed southward as far as the Ohio
River on the east and Yellowstone Park in the west. The Rocky Mountains
and some parts of the Appalachian system accumulated snow and formed
local glaciers, separated from the vast ice-sheet.

The unstable crust of the earth began to sink at length, and gradually
the ice-sheet's progress southward was checked, and it began to recede
by melting. All along the borders of this great fan-shaped ice-field
water accumulated from the melting, and flooded the streams which
drained it to the Atlantic and the Gulf. Icebergs broken off of the edge
of the retiring ice-sheet floated in a great inland sea. The land sank
lower and lower until the general level was five hundred to one thousand
feet lower than it now is. The climate became correspondingly warm, and
the icebergs melted away. Then the land rose again, and in time the
inland sea was drained away into the ocean, except for t