DETAILS OF CURVE PRODUCTION. 57 
wood begins again with the year 1791 in a thick, rapid growth. The 
heartwood continues for some 20 years before changing again into the 
white sapwood, which persists to the outside. In order to make sure 
that this gap would not prevent satisfactory identification, a small 
portion was cut from another part of the outside of the tree, showing 
some 300 rings without interruption; but this additional piece I found 
in that case to be unnecessary. 
In sections numbered 22 and 23, from the old Enterprise millsite, 
there are injuries which do not greatly alter the appearance of the 
rings, yet are sufficiently great to weaken the wood and cause it to 
break at several points. If the break in such case is across the rings, 
it is easy to carry the identity of rings past the injured point. But 
when the break in any wood'sample is all in one ring there may be a 
doubt as to whether the break is between two rings or in the middle of 
one. In the latter case there will apparently be an extra ring at that 
point. If the break is obviously between two complete rings, then an 
unknown number of rings may be lost at the broken point. The only 
way to carry the correct dating of the rings past such broken places is 
to secure samples from other parts of the same tree or from other trees, 
which show 100 to 200 rings on each side of the uncertain place without 
serious interruption. A simple cross-identification will show whether 
any rings are lost. However, in Nos. 22 and 23 just referred to, nearly 
all lines of breakage crossed the rings in a way that left no uncertainty. 
But No. 22 had an injury and a break between complete rings at about 
1020 B. C. and a pronounced injury at about 1060 B. C. No. 23 had 
an extensive decayed place with the loss of about 35 rings at 1060 
B.C. An extra piece cut from the stump of No. 23 carried the dating 
across these gaps with perfect satisfaction and in complete accord with 
No. 21 which had been secured 50 miles to the north. 
Cross-identification between distant points—The sequoias collected 
in 1915 had come from the immediate vicinity of Camp 6, about 7 
miles east of Hume, and from Indian Basin, which is 3 to 4 miles north 
of Hume. The total extent of country covered was about 10 miles. 
All these were identified and found to be very similar in their charac- 
teristics. In 1918 the country represented was extended by sections 
from the new Camp 7, some 2 miles east of Camp 6. Nos. 20 and 21 
were then obtained from the old Converse Hoist, 4 miles from Indian 
Basin and 15 miles from the Camp 7 district. Finally, 2 trees were 
obtained from the old Enterprise millsite, 50 miles from the other 
localities. It was realized at the time that there might be difficulties 
of cross-identification between these 2 trees at Enterprise and the 
other well-known and well-identified groups near Hume and the General 
Grant National Park. However, it was very gratifying to observe 
on close examination of these sections that no uncertainty was intro- 
duced in the identity of the rings. One realizes from this that, so far 
