METHOD OF ESTIMATING RAINFALL BY GROWTH OF TREES. 



107 



trees out of thi-ee which were tested from the Santa Rita Mountains in southeastern Ari- 

 zona, 200 miles from Prescott, were found to have rings which could readily be identified 

 in terms of the Prescott series. 



1880 



1890 



1900 



1910 



Group I 

 Trees 1-10 



Group II 

 Trees 11-35 



Group III 

 Trees 36-50 



Group IV 

 Trees 51-60 



MeHn of 



all trees 



1-60 



1870 1880 1890 1900 1910 



Fio. 9.— Annual Growth of Trees at Prescott, Arizona. 



YEARLY IDENTIFICATION. 



Let us now return to the application of the process of cross-identification to the trees at 

 Prescott. PreUminary to the enumeration of the rings, a particularly clean section was 

 selected and its rings were numbered consecutively; then all the other sections were com- 

 pared with this as a standard. On the completion of 67 sections a careful review was 

 made, and only three cases were found still to be questionable. At that time the following 

 notes were made, the numbers being those obtained by counting back from the outer ring, 

 that is, the ring of 1910: 



" No. 6 frequently double, mostly single, probably really 1 year. 

 Nos. 31 and 32, mostly 1, occasionally clearly 2 years, still in doubt. 

 Nos. 53 and 54 occasionally clearly separate, sometimes very close, often completely 

 merged in one, still in doubt." 



Upon further examination the following occurrences were noted: No. 6 was found 

 double or triple in 46 cases and single in 21, but still uncertain. Nos. 31 and 32 were found 



