86 S. F. Baird on North American Birds. 
brachyrhynchus, Colymbus Pacificus, Bernicla nigricans, Anser 
fiossw, ete. This, however, may be in consequence of their mi- 
grations being along a meridian line, or north and south; the 
meridian of the westernmost point of California and even of 
phemeireaic Island passing east of the mouth of the Mackenzie 
iver. 
In any investigation into the reasons why the eastern province 
is of so much greater extent than the others, and exhibits such 
a trend westward in British America as to reach and even cross 
the Rocky Mountains, we will be greatly aided by the examina- 
tion of Prof. Guyot’s Wall Map of North America. On this 
Lake to the foot of the Rocky Mountains, and north to the Arc- 
tic ocean on both sides of the Mackenzie. Within this vast 
country are “islands” of more elevated land; the whole Appa- 
St. Lawrence system of waters (nearly parallel with the latter), 
the plateau of Iowa and Northern Wisconsin, and that east of 
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Athabasca, and 
Arctic America, and is a great granitic or azoic region, more or less barren of 
Ground Bear, the Polar Hare, and other species. 
