CHAPTER I. 



NOTES UPON GEOGRAPHICAL DISTRIBUTION AND VARIATION WITH REGARD TO 

 THE ZOOLOGY OF THE WESTERN UNITED STATES, AS RELATES MORE 

 PARTICULARLY TO MAMMALS AND BlUDS. 



The subject of the geographical distribution and variation of our west- 

 ern zoology is one that has of late years attracted more than ordinary 

 attention from our naturalists ; and, as appropriate to the subject-matter 

 of this volume, it is here proposed to give a brief resume of their conclu- 

 sions and generalizations, as far as they may be deemed applicable to the 

 special natural history work of the geographical surveys west of the one 

 hundredth meridian. 



It would be hazardous in the extreme to base a series of conclusions or 

 generalizations upon the limited work of this expedition for the last few 

 years ; but enough has been gathered in that period to fully confirm and 

 corroborate the opinions of Professors Baird, Cope, and Allen, and Mr. Ridg- 

 way in this regard. Of these scientists, Prof. J. A. Allen has probably paid 

 more attention to the subject under discussion of late than the others ; 

 and, from his published papers, short excerpta may be permitted more par- 

 ticularly as touching upon mammals and birds.* 



This gentleman, in view of his more recent studies in this line, now 

 considers that we may recognize, in a general way, at least, five more or less 

 well marked areas, characterized by certain peculiarities of variation of col- 

 oration ; and that there exists a correlation between these areas and the 

 prevalent increase of color and the amount of aqueous precipitation. No 

 doubt, other and lesser areas, also characterized by certain similar peculi- 

 arities, will be recognized when a fuller examination of more material is 

 afforded to admit of a careful and prolonged study of the subject. 



* See Proceedings of the Boston Society of Natural History, vol. xvi, February 4, 1874. 



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