19l(i] Dice: Land Ycrtcbrafcs of Southeastern Wasliington 337 



Zones of life are clearly evident upon man.y mountains and in many 

 regions which are not mountainous. The life of the uppermost of some 

 of these mountain zones is evidently related to the life of niore north- 

 ern regions. However, the life of the mountain zones is never identical 

 with the life of any particular northern transcontinental belt. Neither' 

 do the zones found on mountains in different parts of the United States 

 exactly correspond. Grinnell finds the Canadian and Hudsonian life- 

 zones in California to be far less distinct than the other life-zones in 

 the state. Also in California those two life-zones are much less dis- 

 tinct than they are in the northern part of the continent. In the Blue 

 Mountains of Washington it is almost impossible to separate the Hud- 

 sonian life-zone from the Canadian. In the Pine Forest Mountains of 

 Nevada, Taylor (1912, p. 339) recognizes an area which is referred to 

 the Transition life-zone, but which has a "Boreal infusion." It seems 

 that the zones of life found on the upper parts of southern mountains 

 show less affinity to particular northern transcontinental life belts 

 than they do to an alpine or Arctic type of life in general. 



The life-zones of the various parts of the Sonoran region present 

 still greater difficulties in homologizing. In the first place it may be 

 doubted if transcontinental life-zones really show in the best manner 

 the similarities and differences of the faunas in the various parts of 

 the region. Allen (1892, pp. 217-218) has demonstrated that the 

 genera and subgenera of mammals of the arid division of the Sonoran 

 region are more different from those of the humid division, than are 

 those of a northern transcontinental division of the region from those 

 of a southern division. It seems, then, that the first division of the 

 Sonoran region should be into eastern and western sections. 



The zones of the Sonoran region found in the various parts of the 

 western United States are very difficult to correlate. The number of 

 zones to be distinguished is variable and those of different regions do 

 not seem to be exactly homologous. Following Merriam's classification 

 the three life-zones. Transition, Upper Sonoran, and Lower Sonoran 

 have usually been recognized. However, other zones are sometimes 

 apparent. Grinnell and Swarth (1913, p. 217) have split the Transi- 

 tion zone in the San Jacinto area of southern California into an upper 

 and a lower division. In eastern Washington a division of the Transi- 

 tion zone has also been made and these divisions are as distinct as are 

 any other two zones. As an instance of the difficulty of homologizing 

 zones in different regions, we may mention the Columbia Basin prairie 



