very short geological time ago, just before the coming on of that
winter of winters called the glacial period, a vast deluge of molten
rocks poured from many a chasm and crater on the flanks and summit of
the range, filling lake basins and river channels, and obliterating
nearly every existing feature on the northern portion. At length these
all-destroying floods ceased to flow. But while the great volcanic cones
built up along the axis still burned and smoked, the whole Sierra passed
under the domain of ice and snow. Then over the bald, featureless,
fire-blackened mountains, glaciers began to crawl, covering them from
the summits to the sea with a mantle of ice; and then with infinite
deliberation the work went on of sculpturing the range anew. These
mighty agents of erosion, halting never through unnumbered centuries,
crushed and ground the flinty lavas and granites beneath their crystal
folds, wasting and building until in the fullness of time the Sierra was
born again, brought to light nearly as we behold it today, with glaciers
and snow-crushed pines at the top of the range, wheat-fields and
orange-groves at the foot of it.

This change from icy darkness and death to life and beauty was slow, as
we count time, and is still going on, north and south, over all the
world wherever glaciers exist, whether in the form of distinct rivers,
as in Switzerland, Norway, the mountains of Asia, and the Pacific Coast;
or in continuous mantling folds, as in portions of Alaska, Greenland,
Franz-Joseph-Land, Nova Zembla, Spitzbergen, and the lands about the
South Pole. But in no country, as far as I know, may these majestic
changes be studied to better advantage than in the plains and mountains
of California.

Toward the close of the glacial period, when the snow-clouds became less
fertile and the melting waste of sunshine became greater, the lower