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. 
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 (T’suga 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 voleanic 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 pine 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 ame the drying cracks near the year 800 A. D. almost completely interrupt the continuity 
of the rings. 
