150 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



Arctic Hare, and a marmot. Most, if not all, of these forms are 

 of Old World origin. 



The American portion of the great Holarctic region is 

 called by Mr. Lydekker, who uses Wallace's term, the "Cana- 

 dian subregion," and by Dr. Merriam the "Boreal region." Not 

 that there is any difference of principle involved in this varying 

 nomenclature, for Dr. Merriam says : "It so happens that the 

 Boreal element in America resembles that of Eurasia so closely 

 that in the judgment of many eminent authorities the two 

 constitute a single primary region — a view in which I heartily 

 concur." The Canadian or Boreal subregion of the Holarctic 

 is the great belt of coniferous forest, which extends obliquely 

 across North America from Alaska to New England ; its 

 frontier with the Arctic zone is the northern limit of trees and 



Fig. 57. — Arctic Fox in summer dress. — By permission of the N.Y. Zoijlog. Soc. 



it is divided from the Transition zone approximately by the 

 line of latitude 45° N., though with a sinuous course, and it 

 is carried far to the south by the wooded heights of the Appa- 

 lachian, Rocky and Sierra Nevada Mountains, and along the 

 Pacific coast, the mixed character of which has already been 

 explained ; it extends almost to San Francisco. The sub- 



