82 S. F. Baird on North American Birds. 
Colville. 
The western division begins at the western border of the 
eastern, or along the sterile plains of the trans-Mississippi coun- 
try and extends across to the Pacific ocean. The character of the 
ornithological fauna of this division is much the same through _ 
and beyond the Rocky Mountains to the eastern slope of the 
Sierra Nevada and Cascade Mountains of California and Ore- 
gon, but changes somewhat on the western slope and thence to 
the Pacific, and although to a considerable extent uniform, yet 
exhibits some modifications which may warrant a separation — 
into a western and middle division, making three in all, which 
y call provinces, of very unequal extent, and exhibitin 
further modifitsijatie or sepdecuaccs with latitude, as I shall ; 
proceed to explain, taking into consideration the whole con 
tinent north o: Rem iced, i F i 
As previously remar eastern province or division 
idccade from the Atlantic ocean to about the meridian of 100° : 
west from Greenwich, or 23° west from Washington. The line 
of division on the Gulf of Mexico, starts near the eastern rt 
of Texas, perhaps between the Brazos and the Sabine, and fol 
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