RYDBERG : VEGETATIVE LIFE ZONES OF ROCKY MOUNTAINS 489 



terlstic tree of the Submontane forest of eastern Washington, it is 

 better to treat the region of scattered Bull Pines as a zone by 

 itself, although in reality it is only a transition belt between two 

 life zones. 



The belt of chaparral is really the true representative of the 

 hardwood forest of the Alleghanian Zone of the East and the 

 Submontane zone of oaks, chestnuts, and walnuts of Europe. It is 

 true that it is a poor representative thereof, not only as to the 

 size of the trees (or rather shrubs), but also as to the extent of 

 the zone itself. Marcus E. Jones, who has studied the flora of 

 Utah, California, and Arizona, has come to the same conclusion, 

 though other ideas of his regarding limitations of zones and prov- 

 inces are somewhat faulty. A little north of the x'\rkansas Divide 

 (about Lat. 39°) , this belt disappears on the east side of the Rockies. 

 It reaches there its northern limit at the altitude at which the 

 grass-covered plains reach the mountains. The life zone is evi- 

 dently here continued on the plains as grasslands, and naturally the 

 oaks disappear. The hardwood belt reappears partly in the foot- 

 hills of the Black Hills, but here it contains only eastern species, 

 such as Quercus macrocarpa, Ulmus americana, Ostrya virginica, 



etc. 



8. The Great Plains 



The Rockies are bordered on the east by the Plains. These 

 slope, in Colorado and Kansas, about 3,500 feet in 5 degrees of 

 longitude or 10 feet to the mile, i. e., decreasing in altitude from 

 about 6,000 feet to 2,500 feet. In the north the slope is still 

 more gentle, in northern Montana and North Dakota about 2,000 

 feet in 13 degrees or 10 feet in 43^2 miles from about 4,000 to 2,000 

 feet altitude. From this can also be seen that the plains are higher 

 in the south and lower in the north, i. e., that the slope is south- 

 west to northeast. The northern part of the plains Dr. Merriam 

 included in the arid division of the Transition Zone, the southern 

 part in the Upper Sonoran. In this I agree, but I do not 

 agree as to the limitation of these zones. The maps which Dr. 

 Merriam has issued at different times vary a good deal, but in all I 

 have seen the Upper Sonoran Zone is carried to the north into west- 

 ern South Dakota and southeastern Montana and in the one pub- 

 lished in 1898, with his "Life zones and crop zones of the United 

 States,"^ it includes even one third of Montana, Wyoming, and 



1 U. S. Dept. Agr. Div. Biol. Surv. Bull. lo: 1898. 



