et thick even in
Scotland, the ice-sheet that resulted from the fusion of the glaciers
gradually thinned as it went south, and ended in an irregular fringe
across Central Europe. The continent at that time stretched westward
beyond the Hebrides and some two hundred miles beyond Ireland. The
ice-front followed this curve, casting icebergs into the Atlantic, then
probably advanced up what is now the Bristol Channel, and ran across
England and Europe, in a broken line, from Bristol to Poland. South
of this line there were smaller ice-fields round the higher mountains,
north of it almost the whole country presented the appearance that we
find in Greenland to-day.

In North America the glaciation was even more extensive. About four
million square miles of the present temperate zone were buried under ice
and snow. From Greenland, Labrador, and the higher Canadian mountains
the glaciers poured south, until, in the east, the mass of ice
penetrated as far as the valley of the Mississippi. The great lakes of
North America are permanent memorials of its Ice-Age, and over more than
half the country we trace the imprint and the relics of the sheet. South
America, Australia, Tasmania, and New Zealand had their glaciated areas.
North Asia was largely glaciated, but the range of the ice-sheet is not
yet determined in that continent.

This summary statement will convey some idea of the extraordinary
phase through which the earth passed in the early part of the present
geological era. But it must be added that a singular circumstance
prolonged the glacial regime in the northern hemisphere. Modern
geologists speak rather of a series of successive ice-sheets than of one
definite Ice-Age. Some, indeed, speak of a series of Ice-Ages, but we
need not discuss the verbal question. It is now beyond question that the
ice-sheet advanced and retreated several times during the Glacial Epoch.
The American and some English geologists distinguished six ice-sheets,
with five intermediate periods of more temperate climate. The German
and many English and French geologists distinguish four sheets and
three interglacial epochs. The exact number does not concern us, but the
repeated spread of the ice is a point of some importance. The various
sheets differed considerably in extent. The wide range of the ice which
I have described represents the greatest extension of the glaciation,
and probably corresponds to the second or third of the six advances in
Dr.