Transition Zone. 31 



Enu-land (except Maine and the niountuinri of Vermont and New 

 Hani[)shire) and extends westerl}^ over the greater part of New 

 York, southern Ontario, and Pennsylvania, and sends an arm 

 south along the Alleghanies all the way across the Virginias, 

 Carolinas, and eastern Tennessee, to northern Georgia and Ala- 

 l)ama. In the Great T.ake region this zone continues westerly 

 across southern Michigan and Wisconsin, and then curves north- 

 ward over the prairie region of Minnesota, covering the greater 

 parts of North Dakota, Manitoba, and the plains of the Saskatch- 

 ewan ; thence bending abruptly south, it crosses eastern Mon- 

 tana and Wyoming, including parts of western South Dakota 

 and Nebraska, and forms a belt along the eastern base of the 

 Rocky Mountains in Colorado and northern New Mexico, here as 

 elsewhere occupying the interval between the Upper Sonoran and 

 Boreal Zones. 



In Wyoming the Transition Zone passes broadly over the well- 

 known low divide of the Rocky Mountains, which affords the 

 route of the Union Pacific railway, and is directly continuous 

 with the same zone in parts of Colorado, Utah, and Idaho, skirt- 

 ing the Boreal boundaries of the Great Basin all the way around 

 the plains of the Columbia, sending an arm northward over the 

 dry interior of British Columbia, descending along the eastern 

 base of the Cascade Range and the High Sierra to the southern 

 extremity of the latter, and occupying the summits of the Coast 

 Ranges in California and of many of the desert ranj^es of the 

 Great Basin. 



The Transition Zone, as its name indicates, is a zone of over- 

 lapping of Boreal and Sonoran types. Many Boreal genera and 

 species here reach the extreme southern limits of their distribu- 

 tion, and many Sonoran genera and species their northern limits. 

 But a single mammalian genus (Si/nfrptomys) is restricted to the 

 Transition Zone, and future research may show it to inhaljit the 

 Boreal Region also. 



tion of the warm temperate zone and that of the cold temperate zone. 

 * * * Not only is this also the northern limit of the culture of fruit 

 trees, but this zone is equally remarkable for the great variety of elegant 

 shruljs which occur particularly on its northern borders, where we find 

 so great a variety of species belonging to the genera, Celastrus, Crat;egus, 

 Ribes, Cornus, Hamamelis, Vaccinium, Kalmia, Rhodora, Azalea, Rhodo- 

 dendron, Andromeda, Clethra, Viburnum, Cephalanthus, Prinos, Dirca, 

 Celtis, &c." (Lake Superior, 1850, 182-18:',.) 



