And see how some of
the longest of the banners on the highest peaks are streaming perfectly
free from peak to peak across intervening notches or passes, while
others overlap and partly hide one another.
As to their formation, we find that the main causes of the wondrous
beauty and perfection of those we are looking at are the favorable
direction and force of the wind, the abundance of snow-dust, and the
form of the north sides of the peaks. In general, the north sides are
concave in both their horizontal and vertical sections, having been
sculptured into this shape by the residual glaciers that lingered in
the protecting northern shadows, while the sun-beaten south sides,
having never been subjected to this kind of glaciation, are convex or
irregular. It is essential, therefore, not only that the wind should
move with great velocity and steadiness to supply a sufficiently copious
and continuous stream of snow-dust, but that it should come from the
north. No perfect banner is ever hung on the Sierra peaks by the south
wind. Had the gale today blown from the south, leaving the other
conditions unchanged, only swirling, interfering, cloudy drifts would
have been produced; for the snow, instead of being spouted straight up
and over the tops of the peaks in condensed currents to be drawn out as
streamers, would have been driven over the convex southern slopes from
peak to peak like white pearly fog.
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