110 CLIMATIC CYCLES AND TREE GROWTH 



The varves of De Geer and Antevs provide continuous sequences that 

 cover thousands of years. The Permian anhydrites of Udden do the same 

 to a less degree. This anhydrite even with errors up to 2 per cent shows 

 some 1400 years of practical continuity. The longest continuous sequences 

 found by Bradley in the Green River formation of southern Wyoming are 

 less than 100 years. I have no doubt that we have barely touched the valu- 

 able material along these lines that will eventually be available. 



Since the geological material is without actual dating and is not cross- 

 identified, the common way of presenting results from it is in the frequency 

 periodogram; that is, a plot of the frequency of occurrence of cycles of dif- 

 ferent lengths. Such periodograms may be seen in figure 55, where results 

 from widely different sources are compared. 



BURIED TREES 



At Flagstaff, Arizona, in 1904, the writer discovered in an arroyo a tree 

 stump in place buried 16 feet deep in the valley fill. In 1919 and for several 

 years after, with the aid of Dr. E. S. Miller and Major L. F. Brady, a large 

 number of tree sections were secured in the same arroyo from different depths 

 between l£ feet and 16 feet. The annual rings in the logs at shallow depth 

 were of the sort now growing in the pines thereabouts — dry climate rings. 

 The rings at 12 and 16 feet in depth were wet climate rings — large and show- 

 ing a slow surge in size characteristic of a relatively continuous water supply. 

 This contrast occurring in one locality appeared to indicate a climatic change. 

 Ten of these buried trees, chiefly from the upper levels, gave excellent meas- 

 ured records aggregating more than 1400 years. 



These records have been analyzed by the writer from time to time, with 

 the result of finding cycle lengths at 8.5, 10 or a little less, 11^ with indications 

 of a second crest, 14, 17 and 19 years. Mr. Schulman's recent analyses have 

 largely duplicated these results but he has gone very much more into detail. 

 He places a strong cycle maximum at 12 years. This will appear in his lists 

 below and in the frequency periodogram prepared by him and shown in figure 

 55. 



Since the curves are not standardized, it was felt that amplitudes obtained 

 by the usual methods would not be satisfactory. So a qualitative idea of 

 the amplitude is given by the underline number, essentially a weight, in 

 column 2. The letter x in that column indicates a weak cycle. One can 

 keep in mind that specimens numbered 1, 2, and 3 were from the greatest 

 depth, and numbers 11 and 13 were lying near the present flat surface of the 

 valley fill. 



YELLOWSTONE FOSSIL TREES 

 In 1929 and 1930 collection was made of some 38 Tertiary sequoias 

 (Sequoia Langsdorfii) , silicified, from Specimen Ridge in Yellowstone Na- 

 tional Park. These fossils were secured by Messrs. Mason and Reade as 

 nearly as possible from one single horizon of petrified stumps. Probably 

 many of them were living trees at the same time. Like the corresponding 



