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.
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 ponderosa) 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 Flagstaff 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.
- 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.