earth's history have extended far toward the equator,
mantling over vast extents of land and shallow sea. The difference
between the ice streams of the mountains and those which we term
continental depends solely on the areas of the fields and the depth of
the accumulation. In an ordinary Alpine region the _neve_ districts,
where the snow gathers, are relatively small. Owing to the rather
steep slopes, the frozen water is rapidly discharged into the lower
valleys, where it melts away. Both in the _neve_ and in the distinct
glacier of the lower grounds there are, particularly in the latter,
projecting peaks, from which quantities of stone are brought down by
avalanches or in ordinary rock falls, so that the ice is abundantly
supplied with cutting tools, which work from its surface down to its
depths.

As the glacial accumulation grows in depth there are fewer peaks
emerging from it, and the streams which it feeds rise the higher until
they mantle over the divides between the valleys. Thus by
imperceptible stages valley glaciers pass to the larger form, usually
but incorrectly termed continental. We can, indeed, in going from the
mountains in the tropics to the poles, note every step in this
transition, until in Greenland we attain the greatest ice mass in the
world, unless that about the southern pole be more extensive. In the
Greenland glacier the ice sheet covers a vast extent of what is
probably a mountain country, which is certainly of this nature in the
southern part of the island, where alone we find portions of the earth
not completely covered by the deep envelope. Thanks to the labours of
certain hardy explorers, among whom Nansen deserves the foremost
place, we now know something as to the conditions of this vast ice
field, for it has been crossed from shore to shore. The results of
these studies are most interesting, for they afford us a clew as to
the conditions which prevail over a large part of the earth during the
Glacial period from which the planet is just escaping, and in the
earlier ages when glaciation was likewise extensive. We shall
therefore consider in a somewhat detailed way the features which the
Greenland glacier presents.

Starting from the eastern shore of that land, if we may thus term a
region which presents itself mainly in the form of ice, we find next
the shore a coast line not completely covered with ice and snow, but
here and there exhibiting peaks which indicate that if the frozen