Page:Popular Science Monthly Volume 44.djvu/697 THE ICE AGE AND
ITS WORK. By ALFRED K. WALLACE, F. R. S. ERRATIC BLOCKS AND ICE-
SHEETS. IT is little more than fifty years ago that one of the
most potent agents in modifying the surface features of our
country was first recognized. Before 1840, when Agassiz
accompanied Buckland to Scotland, the Lake District, and Wales,
discovering everywhere the same indications of the former
presence of glaciers as are to be found so abundantly in
Switzerland, no geologist had conceived the possibility of a
recent glacial epoch in the temperate portion of the northern
hemisphere. From that year, however, a new science came into
existence, and it was recognized that only by a careful study of
existing glaciers, of the nature of the work they now do, and of
the indications of the work they have done in past ages, could
we explain many curious phenomena that had hitherto been vaguely
regarded as indications of diluvial agency. One of the first
fruits of the new science was the c