Preface. 
165 
The two opposite sections of the state also differ essentially in 
the natural products of the soil, — the southern being clothed 
with almost continuous forests, which in the bottom-lands are 
remarkable for massiveness of growth and great variety of species, 
while in the central and northern portions extensive prairies 
largely prevail. Indeed, it is difficult to conceive of more com- 
plete contrast than that afforded by the cypress swamps, cane- 
brakes, and almost tropical luxuriance of vegetation of the 
southern bottom forests, on the one hand, and the extensive, mon- 
otonous northern prairies on the other. Intervening districts pre- 
sent every conceivable combination of prairie and woodland, while 
particular sections possess special features, such as the line of high 
precipitous bluffs along part of the western border, the romantic, 
almost mountainous range of rugged hills traversing the 
southern portion, from east to west, and the hilly region 
northwestward. The prairies of central and northern Illinois 
being a modified continuation of the “Great Plains,” a consid- 
erable number of birds characteristic of, or peculiar to, the 
“Campestrian District,” together with others common to the 
whole of the Western Region, are thus brought into contact with 
eastern woodland forms; while the proximity of the Great 
Lakes, on the northeast, secures the presence of many species 
formerly considered of purely maritime or littoral habitat, 
but which in reality occur, at one season or another, on 
many of the larger streams of this inland state. Considering 
also in this connection the very large preponderance of the 
southern element in that portion of the state lying south of the 
parallel of 39° (approximately), and also the influx of northern 
forms during the winter season, it may be seen that no less than 
five distinct faunae overlap on the area included within the 
boundaries of the state of Illinois, — the eastern, which, in its 
purity, of course largely predominates; the maritime and 
littoral, by way of the Great Lakes and the St. Lawrence ; the 
boreal, coming down from the high north in winter ; the western, 
extending eastward across the prairies to the border of the 
wooded country; and, lastly, the southern, or “Austroriparian” 
fauna, a very considerable element of which extends up the 
Mississippi valley to at least the 38tli parallel of north latitude. 
