floor more than 380 years, probably thrice as long. The
time-measure in the case is simply this: When the ponderous trunk to
which the old vestige belonged fell, it sunk itself into the ground,
thus making a long, straight ditch, and in the middle of this ditch a
silver fir four feet in diameter and 380 years old was growing, as I
determined by cutting it half through and counting the rings, thus
demonstrating that the remnant of the trunk that made the ditch has lain
on the ground _more_ than 380 years. For it is evident that, to find
the whole time, we must add to the 380 years the time that the vanished
portion of the trunk lay in the ditch before being burned out of the
way, plus the time that passed before the seed from which the monumental
fir sprang fell into the prepared soil and took root. Now, because
sequoia trunks are never wholly consumed in one forest fire, and those
fires recur only at considerable intervals, and because sequoia ditches
after being cleared are often left unplanted for centuries, it becomes
evident that the trunk-remnant in question may probably have lain a
thousand years or more. And this instance is by no means a late one.

Again, admitting that upon those areas supposed to have been once
covered with sequoia forests, every tree may have fallen, and every
trunk may have been burned or buried, leaving not a remnant, many of the
ditches made by the fall of the ponderous trunks, and the bowls made by
their upturning roots, would remain patent for thousands of years after
the last vestige of the trunks that made them had vanished. Much of this
ditch-writing would no doubt be quickly effaced by the flood-action of
overflowing streams and rain-washing; but no inconsiderable portion
would remain enduringly engraved on ridge-tops beyond such destructive
action; for, where all the conditions are favorable, it is almost
imperishable. Now these historic ditches and root-bowls occur in all the
present sequoia groves and forests, but, as far as I have observed, not
the faintest vestige of one presents itself outside of them.

We therefore conclude that the area covered by sequoia has not been
diminished during the last eight or ten thousand years, and probably not
at all in post-glacial time. Nevertheless, the questions may be asked:
Is the species verging toward extinction? What are its relations to
climate, soil, and associated trees?

All the phenomena bearing on these questions also throw light,