Evening star., 1935-11-05

Americas tree-ring calendar. already
extending without break more than
1900 years into the past, is being pushed
back to some Of the earliest traces OF
human habitation on the continent.
DR.. A. E. Douglass of the University Of
Arizona now is at work on floating
chronology" based on timbers recovered
from the rude habitations Of the basket
makers, the primitive race which pre-
ceded the builders of the Pueblos in
the Southwest, 1t is revealed in report
of his work just issued by the National
Geographic Society. The calendar al
ready extends back to the year 698
A. D., and the approximately earliest
ruins of the Pueblo period. Once the
floating chronology of the basket makers
can be established, the next step will be
to make 1t an actual chronology by fill-
ing the gap between it and the Pueblo
period.
A floating chronology" in DR.. Doug
lass terminology, is simply discon-
nected Calendar severed segment Of
history. A considerable number Of tim
bers from some locality are found to
represent a period of years of tree
growth. AS long an unbroken period
as possible is patched together. The
widths of the annual rings tell the
story Of the weather and-by deduction
something of the history Of the people
during this period. But it is not tied
up with anything else. Then comes the
job of searching for other timbers whose
earliest rings overlap the latest rings
on the timbers Of the floating chronology.
Gradually, by this method. the gap grows
smaller until at last some piece Of lum-
ber is found whose latest rings overlap
the earliest rings of the already estab-
lished chronology.
In building up the unbroken chronology
from the earliest Pueblo times to the
present DR.. Douglass, who originally de-
vised the tree ring chronology method,
started with living trees which had been
growing for several hundred years. They
extsnded back approximately to the
beginning Of the historical period when
the Spanish conquistadores first en-
tered the Southwest and found the
Pueblo civilization in it's decline.
Hundreds of old trees showed the same
ring pattern, dependent chiefly on the
varying amounts of rainfall from year
to year. Each year new ring was
added. In wet years this was a wide
ring, in dry years a narrow one. The
widths of individual rings, OF course,
varied from tree to tree, depending on
the species, the vitality of the specimen.
the kind of soil in which 1t grew, and
various other factors. But the pattern
of proportions in the sequence was the
same for all. Thus a chronology could
be established for as far back as these
trees had been growing
Then DR.. Douglass obtained timbers
from the ruins of the great Pueblo
Bonita, one of the greatest in the South
west. The trees from which this timber
had been obtained by the prehistoric
Indians also had been growing at ap-
proximately the same time and conse-
quently different cross-sections would
show the same annual growth pattern.
But Pueblo Bonita was of unknown
antiquity. There was a golf OF time OF
unknown width between it and the old
est trees now growing.
Other Pueblo ruins represented later,
but still prehistoric times. Timbers from
some of them showed patterns which
overlapped the Pueblo Bonita growth
pattern. Others overlapped the period
OF the living trees Slowly, and with
the aid Of three National Geographic
Society expeditions to secure beams from
ruins. DIR. Douglass built up a series
Of links which finally closed the gull.
It vas probably the biggest ana moes