60 CLIMATIC CYCLES AND TREE-GROWTH 



Bonito chronology. It seemed necessary to get some modern trees 

 from that vicinity, so Mr. Morris took me 40 miles north to Basin 

 Mountain, in southwest Colorado, where some 10 different trees were 

 sampled. To these were later added 9 tree sections from a point 

 about 20 miles east of Aztec. These together make a very satisfactory 

 group known in my lists as the "Modern H's," H being the group 

 letter applied to the old Aztec material. 



Chaco Canyon beams — The Aztec sections gave a fine ring record 

 more than 200 years in length, but of unknown date. As soon as its 

 real date becomes known, that much length can be added to the cli- 

 matic record in the southwestern pines. An early shipment of Aztec 

 sections included several from Pueblo Bonito in Chaco Canyon, some 

 50 miles to the south. These specimens came from the American 

 Museum in New York City, where they had been deposited by the 

 Hyde Expedition 25 years before. Very soon these were found to 

 cross-identify with the Aztec sections, and they began to improve and 

 extend that prehistoric record. Then Mr. Neil M. Judd, director of 

 the National Geographic Society Expedition at Pueblo Bonito, became 

 interested in the possibility of developing the chronology of Pueblo 

 Bonito by the ring records and he has collected and sent me nearly 

 160 excellent specimens, mostly from that one ruin. Nearly a hundred 

 of these I have been able to place exactly in the Aztec and Pueblo 

 Bonito chronology. This chronology is referred to as R. D. or relative 

 date, since its true location in our numbering of years, "Anno Domini," 

 is unknown. This Pueblo Bonito material has increased the prehis- 

 toric ring record so that it extends accurately from R. D. 230 to R. D. 

 543, a range of 313 years. A single beam extends it with uncertainties 

 about 40 years later. So if this material could be dated, some 350 

 years of record would be added at one stroke. 



In connection with this collection two trips have been made to 

 Chaco Canyon, one in early September 1922, to get a better knowledge 

 of the beams there and of the problems connected with their dating, 

 and the other in September 1926, to study the living pines in that 

 region. On each occasion many specimens were collected, and on the 

 second trip much was seen of special interest in connection with 

 climatic indicators in trees, which will be mentioned in a later chapter. 



National Geographic Society beam expedition — It is evident that 

 two different interests join in the attempt to date the beams in the 

 ancient ruins of the Southwest, namely, the extension of climatic and 

 solar records in trees, and the archaeological and human interest in 

 the age of those wonderful ruins. For the second reason, the National 

 Geographic Society has encouraged and supported the further collec- 

 tion of early historic and prehistoric material and otherwise assisted 

 in the dating ol these prehistoric beams. In general, two distinct 



