INTRODUCTION 7 



specially mentioned. In connection with this volume, my special thanks are 

 due to Dr. W. S. Glock who made a careful review of the text, to Mr. Edmund 

 Schulman who worked with the author on all cycle problems and whose tests 

 of the analyzing instrument form the major part of the appendix, to Mr. 

 Gordon C. Baldwin, Mr. A. N. Cowperthwait, Mrs. G. Dewey, Mrs. M. B. 

 Koenig, Mrs. E. N. Strickler, and others whose valuable help has made it 

 possible. The photographs of rings in this volume were made in our labora- 

 tories by members of the staff and especially by Mr. H. F. Davis. Land- 

 scapes were mostly taken by members of the staff. The drawings are largely 

 due to Mr. A. J. Krutmeyer and Mr. Davis; cyclograms and special plates 

 were made by Mr. Davis. I am very grateful to Dr. E. B. Wilson, Dr. John 

 A. Fleming, Dr. C. G. Abbot, Mr. H. H. Clayton, Dr. S. B. Nicholson, Dr. 

 D. Alter, Dr. E. F. Carpenter and others for their careful revision of 

 portions of the text. 



NATURE OF TREE-RING DATA 



Trees — Our results have come chiefly from the cone-bearing trees of the 

 Colorado Plateau, the ponderosa or western yellow pine, the Douglas fir, 

 pinyon and juniper, already mentioned on a preceding page. 



Ring Records — Trees are selected from areas in which obvious conserva- 

 tion of water, in brooks or swamps, does not occur; pests and fire effects are 

 avoided. A line is marked from the center to the outside of a cross-section 

 after the radius most free from defects and irregularities has been found; 

 trees with obvious irregularities are not used. Measurements are made of 

 the thickness of the ring, taken in the radial direction. 



Measurements are made to 0.01 mm.; practically all measurements used 

 in this book are considered good to about 0.03 mm., for the rings themselves 

 vary slightly at different points. A few thousand made before 1914 had an 

 average error of 0.06 mm. The series of rings, considered as to thickness, 

 taken in any one radial or part of a radial from the interior out toward the 

 bark is called the ring record of the tree. Obviously, the first fundamental 

 fact deals with the uniformity of record in different parts of the tree. In 

 taking borings in living trees, or in making V-cuts across the ends of logs, or in 

 testing any part of prehistoric logs, or studying fragments of charcoal whose 

 position in the tree is unknown, the value of such measurements clearly 

 depends upon this uniformity throughout the tree. 



Uniformity of record in pines and Douglas firs of the Pueblo area has 

 been found to be fully satisfactory throughout my experience. I have 

 searched thousands of times in the last twenty-five years upon full sections of 

 northern Arizona trees of these species for identity of rings about the circuit, 

 and never, except in the case of obvious injury, have seen any reason what- 

 ever to question a very satisfactory circuit uniformity in the pine and fir that 

 we are using, nor, in fact, in the pinyon, although that is less universal. 



Dissected Trees — In order to make direct tests of uniformity within the 

 trees which we are using for chronological purposes, Dr. Glock and the writer 



