The treeless moorlands and the crags that fill the sky above the
limits of tree-growth form an extensive mountain-top world all by
itself, a realm of plateaus and sky prairies, which only a few have
explored. These regions stand out like islands in the sky; they are
singular treeless expanses above the surrounding forest sea.
This realm is not barren and lifeless. For a number of species it is
home. The ptarmigan and the rose finch, the cony and the bighorn, live
in the heights the year round. Many migrating birds and animals use
the region for a nursery and a summer resort. Here, early in the
autumn, Nature produces her last berries. Here assemble birds from the
lowlands, and flocks from the North stop to feed and frolic while
migrating to the Southland.
Here, too, along with peaks and moorlands, meadows and wild-flower
gardens, are crags, plateaus, cañons, lakes, glaciers, and
snow-fields. Countless small, clear streams originate in these island
heights and from them start merrily down to the far-off seas. Singly
and in clusters, with areas large and areas small, these sky islands
are a feature of most of the National Parks.
[Illustration: ABOVE THE TIMBER-LINE IN THE ROCKY MOUNTAIN NATIONAL
PARK