12 INTRODUCTION. 



America, collections were examined at the Smithsonian Institution in 

 Washington, the horticultural exhibit at the Panama-Pacific Exposition 

 in 1915, the museum at Chicago, but especially the Jessup collection 

 in the American Museum of Natural History in New York City. 

 Much careful counting of rings was done at the latter. 1 



Considering all the trees examined, the conclusion was reached that 

 the conifers, by the great regions they cover, the great variety of 

 climates they endure, and especially by the prominence of their rings, 

 seem best adapted to the purpose in hand. The chief trees, used with 

 approximate number of rings measured in each, are: the yellow pine 

 (Pinus ponderosd) about 14,000; Scotch pine (P. silvestris) about 9,000 ; 

 hemlock (Tsuga canadensis) 2,500; Douglas fir (Pseudotsuga mucronata) 

 2,500; sequoia (Sequoia gigantea) 47,000. 



INTRODUCTION TO SPECIAL STUDIES ON THE YELLOW PINE. 



Before taking up the details of collection and measurement it is 

 desirable to describe certain preliminary studies, such as those upon 

 the yearly identity of the rings, time of the year of ring formation, and 

 so forth. These studies were made chiefly upon the yellow pine of 

 northern Arizona, but from the similarity between the pine and the 

 other trees used it seems safe to say that the results apply equally to the 

 Scotch pine, sequoia, hemlock and other species employed. 



Location. The yellow pines upon which the studies were made 

 were obtained near Flagstaff, in the central part of northern Arizona, 

 at an elevation of about 6,800 feet above the sea. The northern part 

 of the State is largely a plateau forming the southern extension of the 

 great Colorado Plateau. This high area is intersected some 65 miles 

 north of Flagstaff by the Grand Canyon of the Colorado River. South 

 of the town the high elevation extends 50 to 75 miles, varying only a 

 few hundred feet from place to place, and then falls away abruptly at 

 the "Rim." Oak Creek Canyon begins some 10 miles south of Flag- 

 staff and flows to the south into the Verde River. The general drainage 

 nearer town is gently to the northeast into the Little Colorado River 

 some 40 miles away. Ten miles north of town the plateau culminates 

 in the San Francisco Peaks, which reach an elevation of 12,700 feet. 

 This mountain is a finely shaped volcanic mass with the old crater 

 breaking away into a canyon toward the northeast. The town is in 

 latitude 35 N. and longitude 113 W., and lies between two ancient 

 lava streams 200 to 400 feet in height. It has a ' ' wash ' ' flowing through 

 it from north to south, but this carries water only in time of severe 

 storm or of rapidly melting snow. 



1 The 17-foot section of sequoia was reviewed with some care and the dates on it checked. 

 The dating is well done, as the errors are mostly under 15 years. The rings are large an do 

 not show marked variations in width. Much repair work has been done on it, and the pieces of 

 wood filling the drying cracks near the year 800 A. D. almost completely interrupt the continuity 

 of the rings. 



