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Show Delve Into Cliff Dwellers' History PARTIES sent out by the National Nation-al Geographic society and the American Museum of Natural History are digging up ancient buried tree trunks and stumps in Arizona Ari-zona and New Mexico In order to put together a connected history of the Indians In-dians who built pueblos and lived there In a fairly advanced state of civilization civ-ilization centuries ago. An accurate chronology may be worked out, it Is believed, by the method developed by Dr. A. E. Douglass, Doug-lass, professor of astronomy and phy-sIce phy-sIce at the University of Arizona. A cross-section of a modern or ancient tree in the hands of Doctor Douglass is an almanac or annual register of the period in which it lived. When enough burled trees of various ages have been studied it Is believed that an exact year-to-year history of the climate In any given region may be worked out. When this study has been completed the age of various ruins may be fixed exactly by comparing cross-sections of timber found in them with the cross-sections of trees of various vari-ous periods. The rings which appear on the tree between the core and the outer sur face vary from year to year, according to climate and other conditions. The first ring about the core is formed during dur-ing the first year of the tree's life. The second ring encircling the first grows in the following year, and so on. This process has been kept up for more than 3,000 years in some of the giant redwoods of California. The rings are distinctly marked, because the growth Is different in spring and summer from what it Is in the rest of the year. There is a difference in the cell growths of the fall which makes a dark color In the ring, so that each year's growth Is clearly written on the cross-section of the tree. The application of the study of annual an-nual tree rings to history and archeology ar-cheology lies in the fact that ancient beams, rafters and furniture will all show the varying tree ring patterns of the trees from which they were cut. If trees enough are found to trace the irnnual variations back several hundred hun-dred or a few thousand years, a standard stand-ard of comparison would exist which would enable the expert to match an ancient beam or piece of furniture with the ring-pattern of Its period, thus fixing the age almost exactly. |