ADDENDUM.
In the summer of 1919 a trip was made to the sequoia groves with three objects in view: (1) settling an uncertainty regarding the ring provisionally called 1580a; (2) gathering material bearing on the relation of short-period cycles to topography; (3) investigating the causes of enlarged or gross rings. It is only the first of these topics which has an important bearing on the foregoing chapters.
The region near the General Grant National Park was visited and 12 new trees were very carefully selected as to their water-supply, drainage, and distance from other trees, and short radial samples were cut from them. It did not seem necessary to have these include more than the last 500 years of growth. The radial piece, therefore, was made very small, but especial attention was given to procuring a continuous and reliable record. Critical examination showed at once that occurrence of the ring 1580a was dependent on locality. The trees from the uplands, where identification was easy, largely failed to show the ring, but in specimens from swampy basins, where cross-identification was difficult and sometimes uncertain, the ring was nearly always present. A complete decision, therefore, in favor of its real existence was satisfactorily obtained and the necessary corrections were made in the foregoing text and in the tabular matter which follows. It seems likely that the year 1580, which this ring represents, was phenomenally deficient in moisture in the locality of these giant trees.
In addition to the 12 new trees added to the sequoia group, a cutting was made from the stump D-12, which had hitherto defied all attempts at satisfactory dating. A small piece going back about 800 years was cut from a part of the circumference, entirely free from compressed rings, about 4 feet away from the full sample cut in 1915. At the time of cutting, great care was taken to insure proper cross-identification between the inner end of the new piece and the former sample. But in the laboratory the new piece proved to carry a very excellent series of rings and the identification was everywhere very easy and sure, and all doubt about the dating of that particular tree to its earliest ring in 135 A. D., several inches away from its original center, was removed; therefore, it may now be included among those whose dating is entirely reliable.
A new group of 5 very old trees from near Flagstaff, has settled an uncertainty regarding the years 1463 and 1464 in the yellow pines (too late, however, to rectify figure 3 on page 25). It is now possible to carry a very fair cross-identification between the pines of Arizona and the sequoias of California through the whole five centuries of the former.
