56 CLIMATIC CYCLES AND TREE-GROWTH. 
In nearly every decade some are thus distinguished, and in each century 
there are usually 3 to 4 conspicuously small rings which give very 
important aid. 
In the first work on the 2,200-year sequoia record, the identification 
was a laborious task involving all the writer’s spare time for a year. 
The only real difficulty was with the ring for the year 1580. This was 
temporarily called 1580a, but the material collected in 1919 showed it 
to represent a year and a final and complete renumbering included it as 
such. In the end the comparisons gave entire confidence as to the 
identity of every ring. Section No. 2 gave the most nearly perfect 
long record, beginning at 274 B. C., and is used as a standard with 
which to compare all new ones. 
The most difficult parts to identify are the compressed rings. Over 
long periods, varying from 5 or 10 up to 100 years, the rings are some- 
times so crowded together that large numbers of them seem to be 
merged into one and their identification becomes extremely difficult 
and in a few cases impossible. The great variations in sizes so produced 
also exaggerate effects. These groups of compressed rings are con- 
sidered as of little value, and in fact in many trees their measurement 
is omitted altogether. Tree No. 12 of the sequoias obtained from the 
Indian Basin had such bad groups of compressed rings that it proved 
practically impossible to identify them without a large expenditure of 
time not then available. Tree No. 17, also, from Camp 7, was found so 
full of compressed rings in the last few hundred years that all measure- 
ments were omitted after the year 1130 A. D. 
Fire-scars.—Most of the big trees show fire-scars at some time in 
their history, and the process of the tree’s regeneration is very inter- 
esting to observe. If the scar is small the woody growth quickly 
comes in from each side and covers it. If the scar is very large, occupy- 
ing perhaps one-quarter or one-third of the circumference, the tree 
is likely never to recover and the burnt place remains permanently 
on its side. In cases of less extensive burns, the wood from each side 
year by year grows toward and over the injured spot, and if the injury 
has not been too great the approaching sides may meet and imprison 
their own bark within the tree. Thus one often sees the tops of the 
stumps marked here and there by a hole as large as a foot in diameter, 
filled with bark in perfectly good condition. 
No. 12 had several fire-scars that interfered with the identification 
of rings. No. 18 also had one or two fire-scars and in particular showed 
a fire in the year 1781. The latter evidently stopped the growth at 
that point completely, yet was not large enough to interfere with 
recovery. In the sample in the laboratory the usual reddish-colored 
heartwood changes about the year 1700 to the white sapwood, which 
ends with the ring 1781 and shows a surface that was once covered with 
bark. However, immediately outside of that surface, the red heart- 
