IX.] TRANSITION ZONE. 361 



Myodes, Cuniculus, Zapus, Erethizon, Lagomys, Cervus, Alces, 

 Rangifer, and Haploceros. On the other hand, the following, 

 which are as clearly of northern origin, penetrate as far south 

 as the Sonoran region, which some of them enter. These are 

 Sorex, Mustela (only the members of the sub-genus Putorius), 

 Ursus, Fiber, Microtus, Castor, Tamias, Bos, and Ovis. 



Between the Canadian sub-region of the Holarctic and the 

 Sonoran region is interposed a tract whose fauna 

 contains a mixture of Canadian and Sonoran forms, Transition 



Zone. 



and it is consequently termed by Dr Merriam the 

 Transition zone. Under this somewhat indefinite title the area 

 may best be left. It is described by the author just cited as 

 follows 1 : "The humid division of this zone, known as the 

 Alleghanian fauna, covers the greater part of New England (except 

 Maine and the mountains of Vermont and New Hampshire), and 

 extends westerly 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 Alabama. In the 

 Great Lake region this zone continues westerly across southern 

 Michigan and Wisconsin, and then curves northward over the 

 prairie-region of Minnesota, covering the greater parts of North 

 Dakota, Manitoba, and the plains of the Saskatchewan ; thence 

 bending abruptly south, it crosses eastern Montana 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 Canadian 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, Uta, and Idaho, skirting the 

 Canadian 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 



1 Appendix, No. 19, p. 30. In this extract the word Canadian has been 

 substituted for Boreal. 



