130 



CLIMATIC CYCLES AND TREE GROWTH 



were: first, Arizona, including northern Arizona, and New Mexico west of the 

 Rio Grande, and the southern parts of Colorado and Utah; second, the Rocky 

 Mountain area, Rio Grande, then east to include Pike's Peak and the Rockies 

 north to Yellowstone Park; Sante Fe and points near Mesa Verde were in- 

 cluded in this easterly group although they actually show substantial cross- 

 identity with the Arizona area; third, the Coast Zone, including the mountain 

 ranges from points east of San Diego on the south to the Dalles along the 

 Columbia River on the north. The Spring Mountains west of Las Vegas, 

 Nevada, show excellent relation both to Arizona and California . 



These different zones were found to give much the same cycle lengths 

 but with different emphasis in weight or frequencies. It seemed probable 

 that the Rockies showed more subdivisions of 34 or 35 years while the Coast 

 Zone made more use of 23 years and its subdivisions and simple fractions. 

 Arizona partook of each, and so the cycle complex as a whole was plainly 

 based on climatic changes over a large and substantial area and not at all on 

 one tree or one square mile or one state. It becomes a terrestrial affair and 

 seems worth testing in all favorable parts of the earth. It has been found 



Fig. 56 — Western cycles compared to simple fractions of 34 years. 



strongly evident in the coast redwoods though their dating is less secure. 

 It shows in Vermont hemlocks and in Douglas firs on the Oregon coast. 



It was then recognized that the cycle lengths appeared to be simple fractions 

 of small multiples of about 11.3 years. Thus it was seen that they included 

 the secondary or lesser cycles observed in the sunspot numbers. This was the 

 result that was checked by the "unknown scale" method (page 47). The 

 correspondence between originals and values obtained at unknown scale has 

 been shown in "Conferences on Cycles," 1929, and the relation to simple ratios 

 of the sunspot cycle appears in figure 56. 



Complex from Geological Material — In the last chapter the various groups 

 of geological tree rings or sediments were described and their cycle readings 

 discussed. The various analyses of modern and past climates when brought 

 together show two chief results of interest to us. First, all these terrestrial 

 cycles from geological sources approximate in length the cycles in sunspot 

 numbers as well as did those in modern ring records (see fig. 55) ; and second, 

 they exhibit the two types of cycle complex or mixture already observed 

 historically in the sun and trees; namely, the present common type in which 

 an 11.4-year cycle or something near that is conspicuous and the dearth 



