158 ORALLY. 



adapted for them at the seasons when food on these grounds 

 is most abundant and most easily obtained. 



The lower valley of large rivers, especially when these form 

 extensive accumulations of banks, intermingled with pools, 

 are the favourite places, and they are rarely found in the dry 

 countries. The East of Europe from the White Sea, and the 

 flats to the eastward, through Russia, along the shores of the 

 Black Sea, and thence to the valley of the ISTile, as far upward 

 as that river overflows its banks during the rains in Central 

 Africa, form almost one continuous pasture for such birds ; 

 at least, places where they can feed abundantly, according to 

 the season, are at so little distance apart from each other 

 along the whole of it, that the birds (which are, generally 

 speaking, of powerful wing when once they gain their migra- 

 tory elevation) have easy flights from pasture to pasture. The 

 American continent, from the north, down the valleys of the 

 Ohio and Mississippi, and southward to Guiana, and even 

 farther to the southward (for the summit level between the * 

 southern branches of the Amazon and the northern ones of 

 the Plata are flooded during the rains), affords them even a 

 more ample range than they have in the place of their eastern 

 migration. The American continent is also much more 

 humid and much more in a state of nature, so that it is still 

 better adapted to their habits. 



Britain is thus situated, as it were, between two lines of 

 the migrations of those birds, divided from the western one 

 by the wide expanse of the Atlantic, over which we may 

 suppose that the birds have no natural tendency to pass, and 

 that consequently the American ones do not come, and never 

 at any period could have come, except as mere stragglers 

 which had been drifted by cross winds, or had lost their way 

 in the fogs about the Newfoundland banks. The eastern 

 ones are less completely separated from us by any one bar- 



