have been examined. As we shall see hereafter, these features teach us
much as to the conditions of glacial action--a matter which we shall
have to examine after we have completed our general survey as to the
changes which occur during glacial periods.

In the present state of that wonderful complex of actions which we
term climate, glaciers are everywhere, so far as our observations
enable us to judge, generally in process of decrease. In Switzerland,
although the ancients even in Roman days were in contact with the ice,
they were so unobservant that they did not even remark that the ice
was in motion. Only during the last two centuries have we any
observations of a historic sort which are of value to the geologist.
Fortunately, however, the signs written on the rock tell the story,
except for its measurement in terms of years, as clearly as any
records could give it. From this testimony of the rocks we perceive
that in the geological yesterday, though it may have been some tens of
thousands of years ago, the Swiss glaciers, vastly thickened, and with
their horizontal area immensely expanded, stretched over the Alpine
country, so that only here and there did any of the sharper peaks rise
above the surface. These vast glaciers, almost continually united on
their margins, extended so far that every portion of what is now the
Swiss Republic was covered by them. Their front lay on the southern
lowlands of Germany, on the Jura district of France; on the south, it
stretched across the valley of the Po as far as near Milan. We know
this old ice front by the accumulations of rock _débris_ which were
brought to it from the interior of the mountain realm. We can
recognise the peculiar kinds of stone, and with perfect certainty
trace them to the bed rock whence they were riven. Moreover, we can
follow back through the same evidence the stages of retreat of the
glaciers, until they lost their broad continental character and