Like gigantic geysers spouting
molten rock instead of water, volcanoes work and rest, and we have no
sure means of knowing whether they are dead when still, or only
sleeping.
Along the western base of the range a telling series of sedimentary
rocks containing the early history of the Sierra are now being studied.
But leaving for the present these first chapters, we see that only a
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.
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