ROBB^T^'^] CLIMATE AND EVIDENCE OP CLIMATIC CHANGES 57 



Piiion pine and cedar seedlings do occur at the stress zone, although 

 not in greater abundance than at any other point in the forma- 

 tion. The whole aspect of the line of stress between these two 

 formations shows that the pinon pine-cedar formation is encroaching 

 on the rock-pine formation, a condition which would not exist unless 

 there is progressive tlesiccation which is tending to make the debatable 

 territory unfavorable for the rock pines and better suited for piiion 

 pines and cedars. 



Along the Santa Fe railroad in Arizona observations were made 

 which have some bearing on the subject. Between Winslow and 

 Flagstaff the elevation gradually increases from 4,800 feet to 6,800 

 feet. At Angell the juniper belt is well developed, with a few pinon 

 pines between. As the elevation increases, pmon pmes become 

 relatively more abundant, and occasionally large lone rock pines are 

 seen. It is significant that the rock-pme outposts are large individ- 

 uals, scattered here and there. In the neighborhood of these large 

 trees no seedlings were noted; there were, however, numerous piiion 

 pine and cedar seedlings. Many large dead rock pines occur: these 

 do not seem to have been killed by fire or disease, and there are too 

 manj^ of them to ascribe theii- death to lightning. It is not at aU 

 improbable that drought is the cause of the fatality in this case. On 

 the western slope of the divide, after leaving Flagstaff, no such rela- 

 tion as mentioned for the eastern slope exists. Here the outposts 

 of the rock-pine formation are not especially large, nor is there an 

 absence of seedlings at the edge of the formation. 



A thorough study of the vegetal stress zones in the Southwest 

 would untloubtedly shed much light on the question of climatic 

 changes. It is impossible to assign much importance to fragmentary 

 observations, as the foregoing necessarily are, until they are seen in 

 connection with more extensive flata, such as a general study of the 

 Southwest would bring out. 



Any changes which may have occurred during the last few centu- 

 ries should be revealed by an extended study of the growth rings of 

 coniferous trees. ^ Many such trees in New Mexico and Arizona are 

 from 300 to 500 years old, and some doubtless even older. 



Although slight changes have been and still are in progress in the 

 vegetation, pomtmg to the gradual drying of the country, it is not 

 necessary to suppose that these changes have been extended or radi- 

 cal. There is little reason to doubt that the ancient inhabitants who 

 lived in the cliffs along the northern wall of the Frijoles canyon looked 

 out on a stream fringed with cottonwoods, boxelders, birches, and 

 alders, that they saw tall rock pines against the background of the 

 canyon wall, and that the piiion pines and cedars were as familiar to 



• Douglass, A. E., A Method of Approximating Rainfall Over Long Periods and Some Results of its 

 Application, in Science, n. s., xxx^vn, 33, 1913. 



