It appears, therefore, that just where, at a certain
period in the history of the Sierra, the glaciers were not, there the
Sequoia is, and just where the glaciers were, there the Sequoia is not.
What the other conditions may have been that enabled Sequoia to
establish itself upon these oldest and warmest portions of the main
glacial soil-belt, I cannot say. I might venture to state, however, in
this connection, that since the Sequoia forests present a more and more
ancient aspect as they extend southward, I am inclined to think that the
species was distributed from the south, while the Sugar Pine, its great
rival in the northern groves, seems to have come around the head of the
Sacramento valley and down the Sierra from the north; consequently, when
the Sierra soil-beds were first thrown open to preemption on the melting
of the ice-sheet, the Sequoia may have established itself along the
available portions of the south half of the range prior to the arrival
of the Sugar Pine, while the Sugar Pine took possession of the north
half prior to the arrival of Sequoia.
But however much uncertainty may attach to this branch of the question,
there are no obscuring shadows upon the grand general relationship we
have pointed out between the present distribution of Sequoia and the
ancient glaciers of the Sierra.
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